We have carried out X-ray structural analysis of a twin-dendritic benzamide molecule (1), a polym... more We have carried out X-ray structural analysis of a twin-dendritic benzamide molecule (1), a polymer (2) containing the twin-dendritic benzamide molecules as side-groups and their mixtures that form LC phases. While the twin-dendritic benzamide (1) self-organizes into a 2d hexagonal columnar lattice, the polymer (2) self-organizes only into a columnar nematic LC phase with short range 2d hexagonal order. The loosely packed supramolecular columns in the polymer are formed by vesicular four-column supercylinders enclosing the polymer bundles in the core. In mixtures, the polymer (2) acts as a host and (1) as a guest filling the empty regions in (2) to create a perfect four-column bundle host-guest supramolecular dendrimer that co-organizes with (1) into different kinds of columnar LC structures with or without superlattice ordering. The LC phases in the mixtures are an interesting example of self-organization of ordered and disordered regions in a soft condensed matter material. Supported by ONR-DMR-9996288 and NSF-DMR-0102459
2013 Fourth International Conference on Computing, Communications and Networking Technologies (ICCCNT), 2013
ABSTRACT A constant current source is essential for impedance measurement techniques in several b... more ABSTRACT A constant current source is essential for impedance measurement techniques in several biomedical applications. The impedance measurement studies in biomedical applications such as bioelectrical impedance analysis (BIA), electrical impedance plethysmography (IPG), electrical impedance myography (EIM), electrical impedance cardiography (ICG), electrical impedance spectroscopy (EIS), electrical impedance tomography (EIT) all need a high precision impedance measurement circuit with high signal to noise ratio (SNR). Moreover the impedance measurement circuit applied to the biomedical, clinical or medical applications such as human subject studies should have a better patient safety. In this direction a Battery-based Constant Current Source (Bb-CCS) is developed for biomedical applications. The Bb-CCS is developed with a modified Howland current source (MHCS) fed by a battery based power supply (BBPS). The current amplitude, frequency and waveforms are set as the circuit variables which are found as adjustable as per the requirements. The frequency responses, load response, Fast Fourier Transform (FFT) of the Bb-CCS are studied and results show that the Bb-CCS can be suitably used for multifrequency impedance measurement methods in biomedical applications.
We have carried out X-ray structural analysis of a twin-dendritic benzamide molecule (1), a polym... more We have carried out X-ray structural analysis of a twin-dendritic benzamide molecule (1), a polymer (2) containing the twin-dendritic benzamide molecules as side-groups and their mixtures that form LC phases. While the twin-dendritic benzamide (1) self-organizes into a 2d hexagonal columnar lattice, the polymer (2) self-organizes only into a columnar nematic LC phase with short range 2d hexagonal order. The
Abstract A Block Matrix based Multiple Regularization (BMMR) technique is proposed for improving ... more Abstract A Block Matrix based Multiple Regularization (BMMR) technique is proposed for improving conductivity image quality in EIT. The response matrix (JTJ) has been partitioned into several sub-block matrices and the highest eigenvalue of each sub-block matrices ...
AbstractÐThe synthesis and polymerization of two AB 3 tapered, self-assembling methacrylate monom... more AbstractÐThe synthesis and polymerization of two AB 3 tapered, self-assembling methacrylate monomers (12 and 13) based on a ®rst generation semi¯uorinated alkyl-substituted monodendron (i.e. minidendron) are described. These monomers contain either a benzo-15crown-5 derivative, which is incorporated via the esteri®cation of 4 0 -hydroxymethyl-1,4,7,10,13-pentaoxabenzocyclopentadecane or a podant group, which is incorporated via the monoesteri®cation of tetraethylene glycol at its focal point, and both bear polymerizable groups on their periphery. The corresponding polymers (14±16) self-assemble and subsequently self-organize into supramolecular networks, which form a 2-D hexagonal columnar lattice via the¯uorophobic effect. These networks consist of a continuous phase, which is based on the semi¯uorinated, paraf®nic barrier layer and which is perforated in a hexagonal array by ion-selective or ion-active channels constructed from the benzo crown-ether and tetraethylene glycol respectively. The replacement of alkyl groups from the periphery of the tapered monodendrons with semi¯uorinated ones induces the self-assembly and, subsequently, the self-organization into supramolecular networks. These networks form 2-D hexagonal columnar lattices with thermal stability in some cases of up to 1108C. The design of such functional supramolecular systems was inspired by the bilayer¯uid mosaic structure of the cell membrane. The lipid bilayer of the cell membrane, which in its ordered state acts as a barrier to the passage of polar molecules, was replaced with the semi¯uorinated paraf®nic barrier, while the protein-based ionic channels were replaced with benzo-15-crown-5 and tetraethylene glycol based channels. The resulting supramolecular material has the mechanical integrity required for both ion-active and ion-selective nanostructured supramolecular systems. q
Polymerization of 2-methyl-2-oxazoline was carried out using a trifunctional initiator, 2-perbrom... more Polymerization of 2-methyl-2-oxazoline was carried out using a trifunctional initiator, 2-perbromomethyl-2-oxazoline. The degree of polymerization (DP) of the resulting polymer was very close to the feed mole ratio of the monomer to initiator. The number-average molecular weight a, increased linearly with conversion, indicating the living nature of the propagating chain end. 'H NMR and end-group analyses results are consistent with the proposal that the polymer possesses a star-shaped structure.
A new synthetic concept named TERMINI that stands for irreversible TERminator Multifunctional INI... more A new synthetic concept named TERMINI that stands for irreversible TERminator Multifunctional INItiator is reported. Suitable combinations of TERMINI and living polymerizations provide access to strategies for the design and synthesis of unprecedented complex molecular and macromolecular architectures from a diversity of commercial monomers. TERMINI represents a masked multifunctional initiator designed to quantitatively and irreversibly interrupt a chain organic reaction or a living polymerization. After demasking, the TERMINI repeat unit enables the quantitative reinitiation, in the presence or absence of a catalyst, of the same or a different living polymerization or a chain organic reaction in more than one direction, thus becoming a branching point. The demonstration of this concept was made by using a combination of metal-catalyzed living radical polymerization (LRP) and (1,1-dimethylethyl)[[1-[3,5-bis(S-phenyl 4-N,N'-diethylthiocarbamate)phenyl]ethenyl]oxy]dimethylsilane as TERMINI, to elaborate a novel iterative divergent method for the synthesis of dendritic macromolecules based on methyl methacrylate (MMA).
Journal of Polymer Science Part A: Polymer Chemistry, 2005
Our laboratory has reported the elaboration of an iterative strategy for the synthesis of dendrit... more Our laboratory has reported the elaboration of an iterative strategy for the synthesis of dendritic macromolecules from conventional monomers. This synthetic method involves a combination of self-regulated metal-catalyzed living radical polymerization initiated from arenesulfonyl chlorides and an irreversible terminator multifunctional initiator (TERMINI). The previous TERMINI,
-Bis(sulfonyl chlorides) of type (II) containing an acetophenone moiety are prepared via a sequen... more -Bis(sulfonyl chlorides) of type (II) containing an acetophenone moiety are prepared via a sequence of reactions involving in the last step the quantitative oxidative chlorination of diethylaminocarbonylthio or benzylthio groups to give the products as extremely pure compounds. An aromatic tris(sulfonyl chloride) is prepared by a related sequence of reactions. Seven novel aromatic multisulfonyl chlorides containing from 3-8 sulfonyl chloride groups are also prepared by two different multistep methods involving the chlorosulfonation of a precursor containing suitable activated aromatic positions as the last step. -(PERCEC, VIRGIL; BERA, TUSHAR K.; DE, BINOD B.; SANAI, YASUYUKI; SMITH, JASON; HOLERCA, MARIAN N.; BARBOIU, BOGDAN; GRUBBS, ROBERT B.; FRECHET, JEAN M.
The synthesis and polymerization of six AB 3 tapered self-assembling methacrylate monomers (5a, 5... more The synthesis and polymerization of six AB 3 tapered self-assembling methacrylate monomers (5a, 5b, 5c, 5d, 17a, and 17b) based on first generation alkyl substituted benzyl ether monodendrons (i.e., minidendrons) containing oligooxyethylene units at their focal point and the polymerizable group on their periphery are described. The corresponding polymers (6a, 6b, 6c, 6d, 18a, and 18b) self-assemble and subsequently selforganize in supramolecular networks that form a 2-D hexagonal lattice. This network consists of a continuous phase based on a paraffin barrier material perforated in a hexagonal array by ion-active channels constructed from the oligooxyethylenic units protected by the aromatic groups of the taper. Complexation of the oligooxyethylene channels of 6a-d with LiCF 3 SO 3 salt enhances the thermal stability of their hexagonal columnar (φ h ) liquid crystalline phase. The enhancement of the thermal stability of the φ h phase of both monomers and polymers up to 86°C is also achieved by shifting the placement of the polymerizable group from the 3 position to the 4 position of the 3,4,5-trisubstituted AB 3 benzoate monodendrons. The design of these macromolecules was inspired by the bilayer fluid mosaic structure of the cell membrane. The lipid bilayer of the cell membrane that acts in its ordered state as a barrier to the passage of polar molecules was replaced with the paraffinic barrier, while the protein-based ionic channels were replaced with oligooxyethylenic-based channels. The resulted supramolecular material has the mechanical integrity required for the design of ion-active nanostructured supramolecular systems.
This paper demonstrates that miscible blends from water-insoluble polymers, such as poly(2,4,4-tr... more This paper demonstrates that miscible blends from water-insoluble polymers, such as poly(2,4,4-trimethylhexamethylene terephthalamide) (1), methylamine imidized poly(methyl methacrylate) (2), and aromatic poly(ether sulfone) (3) and water-soluble polymers, such as poly(2-ethyl-2-oxazoline) (4) and poly(N-vinyl pyrrolidone) (5), respectively, represent a new class of supramolecular hydrogels. When the degree of polymerization (DP) of the water-soluble polymer is larger than that of water-insoluble polymer, the resulting hydrogels adsorb extremely high amounts of water (i.e., 229 wt % in the case of the hydrogel 1/4) and remain mechanically tough. The high water uptake capability of these blends is explained by a supramolecular network structure generated by H-bonding and/or other noncovalent interactions between the water-insoluble hydrophobic polymer and water-soluble hydrophilic segments as reversible cross-linking points interconnected by hydrophilic water soluble segments. The glass transition temperatures of these hydrogels are tailored via the ratio between the weight percent of the two polymers and by the glass transition temperature of the parent polymers. These supramolecular hydrogels can be processed from melt or solution and maintain excellent mechanical properties both in dry and in the water swollen state. This class of hydrogels is of interest for areas such as membranes, contact lenses, tissue engineering, and other biomedical applications.
A novel Projection Error Propagation-based Regularization (PEPR) method is proposed to improve th... more A novel Projection Error Propagation-based Regularization (PEPR) method is proposed to improve the image quality in Electrical Impedance Tomography (EIT). PEPR method defines the regularization parameter as a function of the projection error developed by difference between experimental measurements and calculated data. The regularization parameter in the reconstruction algorithm gets modified automatically according to the noise level in measured data and ill-posedness of the Hessian matrix. Resistivity imaging of practical phantoms in a Model Based Iterative Image Reconstruction (MoBIIR) algorithm as well as with Electrical Impedance Diffuse Optical Reconstruction Software (EIDORS) with PEPR. The effect of PEPR method is also studied with phantoms with different configurations and with different current injection methods. All the resistivity images reconstructed with PEPR method are compared with the single step regularization (STR) and Modified Levenberg Regularization (LMR) techniques. The results show that, the PEPR technique reduces the projection error and solution error in each iterations both for simulated and experimental data in both the algorithms and improves the reconstructed images with better contrast to noise ratio (CNR), percentage of contrast recovery (PCR), coefficient of contrast (COC) and diametric resistivity profile (DRP).
Here we present the structural characterisation of the self-assembling fluorinated tapered dendro... more Here we present the structural characterisation of the self-assembling fluorinated tapered dendrons that drive the formation of supramolecular columnar liquid crystals with promising optoelectronic properties from a wide range of organic materials. Attaching conducting organic donor or acceptor groups to the apex of the dendrons leads to supramolecular columns that contain in their cores pi-stacks of donors, acceptors or donor-acceptor complexes which are surrounded by helically (with short-range helical order) arranged dendrons, as shown by oriented fiber X-ray diffraction studies. The resulting self-organized materials exhibit high charge carrier mobilities along the column axis in the LC as well as glassy LC states. When we use functionalized dendrons and amorphous polymers carrying compatible side groups, these co-assemble such that the polymer is incorporated in the center of the columns through donor-acceptor interactions with the polymer charge carrier mobility enhanced by many orders of magnitude. The resulting donor-acceptor complex combines the desirable properties of the LCs and the polymers. In addition they yield materials with both high electron and hole mobilities within the same material. This is in contrast to conventional multilayer electronic devices where the electron and hole conducting layers are separated by interfacial regions. We anticipate that this simple and versatile strategy for producing conductive pi-stacks of aromatic groups, surrounded by helical dendrons, will lead to a new class of supramolecular materials suitable for electronic and optoelectronic applications. Supported by ONR-DMR-9996288 and NSF-DMR-0102459
Angewandte Chemie International Edition, Jul 25, 2005
Amphiphilic dendrons that adopt the shape of a disk or disk fragment can self-assemble into supra... more Amphiphilic dendrons that adopt the shape of a disk or disk fragment can self-assemble into supramolecular columns which self-organize into p6mm hexagonal or p2mm and c2mm rectangular 2D periodic assemblies.1, 2 The apex of such dendrons generates the hollow1l or ...
Journal of Medical Imaging and Health Informatics, 2014
ABSTRACT Electrical Impedance Tomography (EIT) is a computerized medical imaging technique which ... more ABSTRACT Electrical Impedance Tomography (EIT) is a computerized medical imaging technique which reconstructs the electrical impedance images of a domain under test from the boundary voltage–current data measured by an EIT electronic instrumentation using an image reconstruction algorithm. Being a computed tomography technique, EIT injects a constant current to the patient's body through the surface electrodes surrounding the domain to be imaged ( ) and tries to calculate the spatial distribution of electrical conductivity or resistivity of the closed conducting domain using the potentials developed at the domain boundary ( ). Practical phantoms are essentially required to study, test and calibrate a medical EIT system for certifying the system before applying it on patients for diagnostic imaging. Therefore, the EIT phantoms are essentially required to generate boundary data for studying and assessing the instrumentation and inverse solvers a in EIT. For proper assessment of an inverse solver of a 2D EIT system, a perfect 2D practical phantom is required. As the practical phantoms are the assemblies of the objects with 3D geometries, the developing of a practical 2D-phantom is a great challenge and therefore, the boundary data generated from the practical phantoms with 3D geometry are found inappropriate for assessing a 2D inverse solver. Furthermore, the boundary data errors contributed by the instrumentation are also difficult to separate from the errors developed by the 3D phantoms. Hence, the errorless boundary data are found essential to assess the inverse solver in 2D EIT. In this direction, a MatLAB-based Virtual Phantom for 2D EIT (MatVP2DEIT) is developed to generate accurate boundary data for assessing the 2D-EIT inverse solvers and the image reconstruction accuracy. MatVP2DEIT is a MatLAB-based computer program which simulates a phantom in computer and generates the boundary potential data as the outputs by using the combinations of different phantom parameters as the inputs to the program. Phantom diameter, inhomogeneity geometry (shape, size and position), number of inhomogeneities, applied current magnitude, background resistivity, inhomogeneity resistivity all are set as the phantom variables which are provided as the input parameters to the MatVP2DEIT for simulating different phantom configurations. A constant current injection is simulated at the phantom boundary with different current injection protocols and boundary potential data are calculated. Boundary data sets are generated with different phantom configurations obtained with the different combinations of the phantom variables and the resistivity images are reconstructed using EIDORS. Boundary data of the virtual phantoms, containing inhomogeneities with complex geometries, are also generated for different current injection patterns using MatVP2DEIT and the resistivity imaging is studied. The effect of regularization method on the image reconstruction is also studied with the data generated by MatVP2DEIT. Resistivity images are evaluated by studying the resistivity parameters and contrast parameters estimated from the elemental resistivity profiles of the reconstructed phantom domain. Results show that the MatVP2DEIT generates accurate boundary data for different types of single or multiple objects which are efficient and accurate enough to reconstruct the resistivity images in EIDORS. The spatial resolution studies show that, the resistivity imaging conducted with the boundary data generated by MatVP2DEIT with 2048 elements, can reconstruct two circular inhomogeneities placed with a minimum distance (boundary to boundary) of 2 mm. It is also observed that, in MatVP2DEIT with 2048 elements, the boundary data generated for a phantom with a circular inhomogeneity of a diameter less than 7% of that of the phantom domain can produce resistivity images in EIDORS with a 1968 element mesh. Results also show that the MatVP2DEIT accurately generates the boundary data for neighbouring, opposite reference and trigonometric current patterns which are very suitable for resistivity reconstruction studies. MatVP2DEIT generated data are also found suitable for studying the effect of the different regularization methods on reconstruction process. Comparing the reconstructed image with an original geometry made in MatVP2DEIT, it would be easier to study the resistivity imaging procedures as well as the inverse solver performance. Using the proposed MatVP2DEIT software with modified domains, the cross sectional anatomy of a number of body parts can be simulated in PC and the impedance image reconstruction of human anatomy can be studied.
When we use a conductive fabric as a pressure sensor, it is necessary to quantitatively understan... more When we use a conductive fabric as a pressure sensor, it is necessary to quantitatively understand its electromechanical property related with the applied pressure. We investigated electromechanical properties of three different conductive fabrics using the electrical impedance spectroscopy (EIS). We found that their electrical impedance spectra depend not only on the electrical properties of the conductive yarns, but also on their weaving structures. When we apply a mechanical tension or compression, there occur structural deformations in the conductive fabrics altering their apparent electrical impedance spectra. For a stretchable conductive fabric, the impedance magnitude increased or decreased under tension or compression, respectively. For an almost non-stretchable conductive fabric, both tension and compression resulted in decreased impedance values since the applied tension failed to elongate the fabric. To measure both tension and compression separately, it is desirable to use a stretchable conductive fabric. For any conductive fabric chosen as a pressure-sensing material, its resistivity under no loading conditions must be carefully chosen since it determines a measurable range of the impedance values subject to different amounts of loadings. We suggest the EIS method to characterize the electromechanical property of a conductive fabric in designing a thin and flexible fabric pressure sensor.
Abstract. A Model Based Iterative Image Reconstruction (MoBIIR) algorithm is developed for impeda... more Abstract. A Model Based Iterative Image Reconstruction (MoBIIR) algorithm is developed for impedance image reconstruction of Electrical Impedance Tomography (EIT). Simulated boundary data are generated for circular phantom configuration and the conductivity ...
The resistivity of biological tissue happens to be the basis of the field distribution inside the... more The resistivity of biological tissue happens to be the basis of the field distribution inside the tissue. Hence the current injected in different patterns has a unique current distribution profile. The images of this field distribution are reconstructed using tools like FEMM and EIDORS. The work described here is the EIT based imaging of a closed phantom for detection of abnormality present. This system consists of 16 silver electrodes placed equidistant and detects non-conducting and conducting objects like clay and copper spindle in normal saline solution. The current is injected in two adjacent electrodes and the voltages are measured in neighbouring pattern at every consecutive pair of electrodes. The output data sets are used to reconstruct the voltage density distribution in closed phantom. The resulting images show that the resistivity profiles of the phantom for various events are successfully reconstructed. In this paper, the voltage density distribution is reconstructed into an image to detect the type, the location and the size of the abnormality present using FEMM tool.
2011 World Congress on Information and Communication Technologies, 2011
Conductivity image reconstruction is studied with a Block Matrix based Multiple Regularization (B... more Conductivity image reconstruction is studied with a Block Matrix based Multiple Regularization (BMMR) technique in Electrical Impedance Tomography (EIT) using practical phantoms. The response matrix (JTJ) is partitioned into several sub-block matrices and the largest element of each sub-block matrices is taken as regularization parameter for the nodes of the FEM mesh contained by that sub-block. Boundary potential data are
We have carried out X-ray structural analysis of a twin-dendritic benzamide molecule (1), a polym... more We have carried out X-ray structural analysis of a twin-dendritic benzamide molecule (1), a polymer (2) containing the twin-dendritic benzamide molecules as side-groups and their mixtures that form LC phases. While the twin-dendritic benzamide (1) self-organizes into a 2d hexagonal columnar lattice, the polymer (2) self-organizes only into a columnar nematic LC phase with short range 2d hexagonal order. The loosely packed supramolecular columns in the polymer are formed by vesicular four-column supercylinders enclosing the polymer bundles in the core. In mixtures, the polymer (2) acts as a host and (1) as a guest filling the empty regions in (2) to create a perfect four-column bundle host-guest supramolecular dendrimer that co-organizes with (1) into different kinds of columnar LC structures with or without superlattice ordering. The LC phases in the mixtures are an interesting example of self-organization of ordered and disordered regions in a soft condensed matter material. Supported by ONR-DMR-9996288 and NSF-DMR-0102459
2013 Fourth International Conference on Computing, Communications and Networking Technologies (ICCCNT), 2013
ABSTRACT A constant current source is essential for impedance measurement techniques in several b... more ABSTRACT A constant current source is essential for impedance measurement techniques in several biomedical applications. The impedance measurement studies in biomedical applications such as bioelectrical impedance analysis (BIA), electrical impedance plethysmography (IPG), electrical impedance myography (EIM), electrical impedance cardiography (ICG), electrical impedance spectroscopy (EIS), electrical impedance tomography (EIT) all need a high precision impedance measurement circuit with high signal to noise ratio (SNR). Moreover the impedance measurement circuit applied to the biomedical, clinical or medical applications such as human subject studies should have a better patient safety. In this direction a Battery-based Constant Current Source (Bb-CCS) is developed for biomedical applications. The Bb-CCS is developed with a modified Howland current source (MHCS) fed by a battery based power supply (BBPS). The current amplitude, frequency and waveforms are set as the circuit variables which are found as adjustable as per the requirements. The frequency responses, load response, Fast Fourier Transform (FFT) of the Bb-CCS are studied and results show that the Bb-CCS can be suitably used for multifrequency impedance measurement methods in biomedical applications.
We have carried out X-ray structural analysis of a twin-dendritic benzamide molecule (1), a polym... more We have carried out X-ray structural analysis of a twin-dendritic benzamide molecule (1), a polymer (2) containing the twin-dendritic benzamide molecules as side-groups and their mixtures that form LC phases. While the twin-dendritic benzamide (1) self-organizes into a 2d hexagonal columnar lattice, the polymer (2) self-organizes only into a columnar nematic LC phase with short range 2d hexagonal order. The
Abstract A Block Matrix based Multiple Regularization (BMMR) technique is proposed for improving ... more Abstract A Block Matrix based Multiple Regularization (BMMR) technique is proposed for improving conductivity image quality in EIT. The response matrix (JTJ) has been partitioned into several sub-block matrices and the highest eigenvalue of each sub-block matrices ...
AbstractÐThe synthesis and polymerization of two AB 3 tapered, self-assembling methacrylate monom... more AbstractÐThe synthesis and polymerization of two AB 3 tapered, self-assembling methacrylate monomers (12 and 13) based on a ®rst generation semi¯uorinated alkyl-substituted monodendron (i.e. minidendron) are described. These monomers contain either a benzo-15crown-5 derivative, which is incorporated via the esteri®cation of 4 0 -hydroxymethyl-1,4,7,10,13-pentaoxabenzocyclopentadecane or a podant group, which is incorporated via the monoesteri®cation of tetraethylene glycol at its focal point, and both bear polymerizable groups on their periphery. The corresponding polymers (14±16) self-assemble and subsequently self-organize into supramolecular networks, which form a 2-D hexagonal columnar lattice via the¯uorophobic effect. These networks consist of a continuous phase, which is based on the semi¯uorinated, paraf®nic barrier layer and which is perforated in a hexagonal array by ion-selective or ion-active channels constructed from the benzo crown-ether and tetraethylene glycol respectively. The replacement of alkyl groups from the periphery of the tapered monodendrons with semi¯uorinated ones induces the self-assembly and, subsequently, the self-organization into supramolecular networks. These networks form 2-D hexagonal columnar lattices with thermal stability in some cases of up to 1108C. The design of such functional supramolecular systems was inspired by the bilayer¯uid mosaic structure of the cell membrane. The lipid bilayer of the cell membrane, which in its ordered state acts as a barrier to the passage of polar molecules, was replaced with the semi¯uorinated paraf®nic barrier, while the protein-based ionic channels were replaced with benzo-15-crown-5 and tetraethylene glycol based channels. The resulting supramolecular material has the mechanical integrity required for both ion-active and ion-selective nanostructured supramolecular systems. q
Polymerization of 2-methyl-2-oxazoline was carried out using a trifunctional initiator, 2-perbrom... more Polymerization of 2-methyl-2-oxazoline was carried out using a trifunctional initiator, 2-perbromomethyl-2-oxazoline. The degree of polymerization (DP) of the resulting polymer was very close to the feed mole ratio of the monomer to initiator. The number-average molecular weight a, increased linearly with conversion, indicating the living nature of the propagating chain end. 'H NMR and end-group analyses results are consistent with the proposal that the polymer possesses a star-shaped structure.
A new synthetic concept named TERMINI that stands for irreversible TERminator Multifunctional INI... more A new synthetic concept named TERMINI that stands for irreversible TERminator Multifunctional INItiator is reported. Suitable combinations of TERMINI and living polymerizations provide access to strategies for the design and synthesis of unprecedented complex molecular and macromolecular architectures from a diversity of commercial monomers. TERMINI represents a masked multifunctional initiator designed to quantitatively and irreversibly interrupt a chain organic reaction or a living polymerization. After demasking, the TERMINI repeat unit enables the quantitative reinitiation, in the presence or absence of a catalyst, of the same or a different living polymerization or a chain organic reaction in more than one direction, thus becoming a branching point. The demonstration of this concept was made by using a combination of metal-catalyzed living radical polymerization (LRP) and (1,1-dimethylethyl)[[1-[3,5-bis(S-phenyl 4-N,N'-diethylthiocarbamate)phenyl]ethenyl]oxy]dimethylsilane as TERMINI, to elaborate a novel iterative divergent method for the synthesis of dendritic macromolecules based on methyl methacrylate (MMA).
Journal of Polymer Science Part A: Polymer Chemistry, 2005
Our laboratory has reported the elaboration of an iterative strategy for the synthesis of dendrit... more Our laboratory has reported the elaboration of an iterative strategy for the synthesis of dendritic macromolecules from conventional monomers. This synthetic method involves a combination of self-regulated metal-catalyzed living radical polymerization initiated from arenesulfonyl chlorides and an irreversible terminator multifunctional initiator (TERMINI). The previous TERMINI,
-Bis(sulfonyl chlorides) of type (II) containing an acetophenone moiety are prepared via a sequen... more -Bis(sulfonyl chlorides) of type (II) containing an acetophenone moiety are prepared via a sequence of reactions involving in the last step the quantitative oxidative chlorination of diethylaminocarbonylthio or benzylthio groups to give the products as extremely pure compounds. An aromatic tris(sulfonyl chloride) is prepared by a related sequence of reactions. Seven novel aromatic multisulfonyl chlorides containing from 3-8 sulfonyl chloride groups are also prepared by two different multistep methods involving the chlorosulfonation of a precursor containing suitable activated aromatic positions as the last step. -(PERCEC, VIRGIL; BERA, TUSHAR K.; DE, BINOD B.; SANAI, YASUYUKI; SMITH, JASON; HOLERCA, MARIAN N.; BARBOIU, BOGDAN; GRUBBS, ROBERT B.; FRECHET, JEAN M.
The synthesis and polymerization of six AB 3 tapered self-assembling methacrylate monomers (5a, 5... more The synthesis and polymerization of six AB 3 tapered self-assembling methacrylate monomers (5a, 5b, 5c, 5d, 17a, and 17b) based on first generation alkyl substituted benzyl ether monodendrons (i.e., minidendrons) containing oligooxyethylene units at their focal point and the polymerizable group on their periphery are described. The corresponding polymers (6a, 6b, 6c, 6d, 18a, and 18b) self-assemble and subsequently selforganize in supramolecular networks that form a 2-D hexagonal lattice. This network consists of a continuous phase based on a paraffin barrier material perforated in a hexagonal array by ion-active channels constructed from the oligooxyethylenic units protected by the aromatic groups of the taper. Complexation of the oligooxyethylene channels of 6a-d with LiCF 3 SO 3 salt enhances the thermal stability of their hexagonal columnar (φ h ) liquid crystalline phase. The enhancement of the thermal stability of the φ h phase of both monomers and polymers up to 86°C is also achieved by shifting the placement of the polymerizable group from the 3 position to the 4 position of the 3,4,5-trisubstituted AB 3 benzoate monodendrons. The design of these macromolecules was inspired by the bilayer fluid mosaic structure of the cell membrane. The lipid bilayer of the cell membrane that acts in its ordered state as a barrier to the passage of polar molecules was replaced with the paraffinic barrier, while the protein-based ionic channels were replaced with oligooxyethylenic-based channels. The resulted supramolecular material has the mechanical integrity required for the design of ion-active nanostructured supramolecular systems.
This paper demonstrates that miscible blends from water-insoluble polymers, such as poly(2,4,4-tr... more This paper demonstrates that miscible blends from water-insoluble polymers, such as poly(2,4,4-trimethylhexamethylene terephthalamide) (1), methylamine imidized poly(methyl methacrylate) (2), and aromatic poly(ether sulfone) (3) and water-soluble polymers, such as poly(2-ethyl-2-oxazoline) (4) and poly(N-vinyl pyrrolidone) (5), respectively, represent a new class of supramolecular hydrogels. When the degree of polymerization (DP) of the water-soluble polymer is larger than that of water-insoluble polymer, the resulting hydrogels adsorb extremely high amounts of water (i.e., 229 wt % in the case of the hydrogel 1/4) and remain mechanically tough. The high water uptake capability of these blends is explained by a supramolecular network structure generated by H-bonding and/or other noncovalent interactions between the water-insoluble hydrophobic polymer and water-soluble hydrophilic segments as reversible cross-linking points interconnected by hydrophilic water soluble segments. The glass transition temperatures of these hydrogels are tailored via the ratio between the weight percent of the two polymers and by the glass transition temperature of the parent polymers. These supramolecular hydrogels can be processed from melt or solution and maintain excellent mechanical properties both in dry and in the water swollen state. This class of hydrogels is of interest for areas such as membranes, contact lenses, tissue engineering, and other biomedical applications.
A novel Projection Error Propagation-based Regularization (PEPR) method is proposed to improve th... more A novel Projection Error Propagation-based Regularization (PEPR) method is proposed to improve the image quality in Electrical Impedance Tomography (EIT). PEPR method defines the regularization parameter as a function of the projection error developed by difference between experimental measurements and calculated data. The regularization parameter in the reconstruction algorithm gets modified automatically according to the noise level in measured data and ill-posedness of the Hessian matrix. Resistivity imaging of practical phantoms in a Model Based Iterative Image Reconstruction (MoBIIR) algorithm as well as with Electrical Impedance Diffuse Optical Reconstruction Software (EIDORS) with PEPR. The effect of PEPR method is also studied with phantoms with different configurations and with different current injection methods. All the resistivity images reconstructed with PEPR method are compared with the single step regularization (STR) and Modified Levenberg Regularization (LMR) techniques. The results show that, the PEPR technique reduces the projection error and solution error in each iterations both for simulated and experimental data in both the algorithms and improves the reconstructed images with better contrast to noise ratio (CNR), percentage of contrast recovery (PCR), coefficient of contrast (COC) and diametric resistivity profile (DRP).
Here we present the structural characterisation of the self-assembling fluorinated tapered dendro... more Here we present the structural characterisation of the self-assembling fluorinated tapered dendrons that drive the formation of supramolecular columnar liquid crystals with promising optoelectronic properties from a wide range of organic materials. Attaching conducting organic donor or acceptor groups to the apex of the dendrons leads to supramolecular columns that contain in their cores pi-stacks of donors, acceptors or donor-acceptor complexes which are surrounded by helically (with short-range helical order) arranged dendrons, as shown by oriented fiber X-ray diffraction studies. The resulting self-organized materials exhibit high charge carrier mobilities along the column axis in the LC as well as glassy LC states. When we use functionalized dendrons and amorphous polymers carrying compatible side groups, these co-assemble such that the polymer is incorporated in the center of the columns through donor-acceptor interactions with the polymer charge carrier mobility enhanced by many orders of magnitude. The resulting donor-acceptor complex combines the desirable properties of the LCs and the polymers. In addition they yield materials with both high electron and hole mobilities within the same material. This is in contrast to conventional multilayer electronic devices where the electron and hole conducting layers are separated by interfacial regions. We anticipate that this simple and versatile strategy for producing conductive pi-stacks of aromatic groups, surrounded by helical dendrons, will lead to a new class of supramolecular materials suitable for electronic and optoelectronic applications. Supported by ONR-DMR-9996288 and NSF-DMR-0102459
Angewandte Chemie International Edition, Jul 25, 2005
Amphiphilic dendrons that adopt the shape of a disk or disk fragment can self-assemble into supra... more Amphiphilic dendrons that adopt the shape of a disk or disk fragment can self-assemble into supramolecular columns which self-organize into p6mm hexagonal or p2mm and c2mm rectangular 2D periodic assemblies.1, 2 The apex of such dendrons generates the hollow1l or ...
Journal of Medical Imaging and Health Informatics, 2014
ABSTRACT Electrical Impedance Tomography (EIT) is a computerized medical imaging technique which ... more ABSTRACT Electrical Impedance Tomography (EIT) is a computerized medical imaging technique which reconstructs the electrical impedance images of a domain under test from the boundary voltage–current data measured by an EIT electronic instrumentation using an image reconstruction algorithm. Being a computed tomography technique, EIT injects a constant current to the patient's body through the surface electrodes surrounding the domain to be imaged ( ) and tries to calculate the spatial distribution of electrical conductivity or resistivity of the closed conducting domain using the potentials developed at the domain boundary ( ). Practical phantoms are essentially required to study, test and calibrate a medical EIT system for certifying the system before applying it on patients for diagnostic imaging. Therefore, the EIT phantoms are essentially required to generate boundary data for studying and assessing the instrumentation and inverse solvers a in EIT. For proper assessment of an inverse solver of a 2D EIT system, a perfect 2D practical phantom is required. As the practical phantoms are the assemblies of the objects with 3D geometries, the developing of a practical 2D-phantom is a great challenge and therefore, the boundary data generated from the practical phantoms with 3D geometry are found inappropriate for assessing a 2D inverse solver. Furthermore, the boundary data errors contributed by the instrumentation are also difficult to separate from the errors developed by the 3D phantoms. Hence, the errorless boundary data are found essential to assess the inverse solver in 2D EIT. In this direction, a MatLAB-based Virtual Phantom for 2D EIT (MatVP2DEIT) is developed to generate accurate boundary data for assessing the 2D-EIT inverse solvers and the image reconstruction accuracy. MatVP2DEIT is a MatLAB-based computer program which simulates a phantom in computer and generates the boundary potential data as the outputs by using the combinations of different phantom parameters as the inputs to the program. Phantom diameter, inhomogeneity geometry (shape, size and position), number of inhomogeneities, applied current magnitude, background resistivity, inhomogeneity resistivity all are set as the phantom variables which are provided as the input parameters to the MatVP2DEIT for simulating different phantom configurations. A constant current injection is simulated at the phantom boundary with different current injection protocols and boundary potential data are calculated. Boundary data sets are generated with different phantom configurations obtained with the different combinations of the phantom variables and the resistivity images are reconstructed using EIDORS. Boundary data of the virtual phantoms, containing inhomogeneities with complex geometries, are also generated for different current injection patterns using MatVP2DEIT and the resistivity imaging is studied. The effect of regularization method on the image reconstruction is also studied with the data generated by MatVP2DEIT. Resistivity images are evaluated by studying the resistivity parameters and contrast parameters estimated from the elemental resistivity profiles of the reconstructed phantom domain. Results show that the MatVP2DEIT generates accurate boundary data for different types of single or multiple objects which are efficient and accurate enough to reconstruct the resistivity images in EIDORS. The spatial resolution studies show that, the resistivity imaging conducted with the boundary data generated by MatVP2DEIT with 2048 elements, can reconstruct two circular inhomogeneities placed with a minimum distance (boundary to boundary) of 2 mm. It is also observed that, in MatVP2DEIT with 2048 elements, the boundary data generated for a phantom with a circular inhomogeneity of a diameter less than 7% of that of the phantom domain can produce resistivity images in EIDORS with a 1968 element mesh. Results also show that the MatVP2DEIT accurately generates the boundary data for neighbouring, opposite reference and trigonometric current patterns which are very suitable for resistivity reconstruction studies. MatVP2DEIT generated data are also found suitable for studying the effect of the different regularization methods on reconstruction process. Comparing the reconstructed image with an original geometry made in MatVP2DEIT, it would be easier to study the resistivity imaging procedures as well as the inverse solver performance. Using the proposed MatVP2DEIT software with modified domains, the cross sectional anatomy of a number of body parts can be simulated in PC and the impedance image reconstruction of human anatomy can be studied.
When we use a conductive fabric as a pressure sensor, it is necessary to quantitatively understan... more When we use a conductive fabric as a pressure sensor, it is necessary to quantitatively understand its electromechanical property related with the applied pressure. We investigated electromechanical properties of three different conductive fabrics using the electrical impedance spectroscopy (EIS). We found that their electrical impedance spectra depend not only on the electrical properties of the conductive yarns, but also on their weaving structures. When we apply a mechanical tension or compression, there occur structural deformations in the conductive fabrics altering their apparent electrical impedance spectra. For a stretchable conductive fabric, the impedance magnitude increased or decreased under tension or compression, respectively. For an almost non-stretchable conductive fabric, both tension and compression resulted in decreased impedance values since the applied tension failed to elongate the fabric. To measure both tension and compression separately, it is desirable to use a stretchable conductive fabric. For any conductive fabric chosen as a pressure-sensing material, its resistivity under no loading conditions must be carefully chosen since it determines a measurable range of the impedance values subject to different amounts of loadings. We suggest the EIS method to characterize the electromechanical property of a conductive fabric in designing a thin and flexible fabric pressure sensor.
Abstract. A Model Based Iterative Image Reconstruction (MoBIIR) algorithm is developed for impeda... more Abstract. A Model Based Iterative Image Reconstruction (MoBIIR) algorithm is developed for impedance image reconstruction of Electrical Impedance Tomography (EIT). Simulated boundary data are generated for circular phantom configuration and the conductivity ...
The resistivity of biological tissue happens to be the basis of the field distribution inside the... more The resistivity of biological tissue happens to be the basis of the field distribution inside the tissue. Hence the current injected in different patterns has a unique current distribution profile. The images of this field distribution are reconstructed using tools like FEMM and EIDORS. The work described here is the EIT based imaging of a closed phantom for detection of abnormality present. This system consists of 16 silver electrodes placed equidistant and detects non-conducting and conducting objects like clay and copper spindle in normal saline solution. The current is injected in two adjacent electrodes and the voltages are measured in neighbouring pattern at every consecutive pair of electrodes. The output data sets are used to reconstruct the voltage density distribution in closed phantom. The resulting images show that the resistivity profiles of the phantom for various events are successfully reconstructed. In this paper, the voltage density distribution is reconstructed into an image to detect the type, the location and the size of the abnormality present using FEMM tool.
2011 World Congress on Information and Communication Technologies, 2011
Conductivity image reconstruction is studied with a Block Matrix based Multiple Regularization (B... more Conductivity image reconstruction is studied with a Block Matrix based Multiple Regularization (BMMR) technique in Electrical Impedance Tomography (EIT) using practical phantoms. The response matrix (JTJ) is partitioned into several sub-block matrices and the largest element of each sub-block matrices is taken as regularization parameter for the nodes of the FEM mesh contained by that sub-block. Boundary potential data are
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Papers by Tushar K Bera