Papers by Dale W. Schaefer
Oxford University Press eBooks, Apr 2, 2015
The polysiloxane of greatest commercial importance and scientific interest is poly(dimethylsiloxa... more The polysiloxane of greatest commercial importance and scientific interest is poly(dimethylsiloxane) (PDMS), [Si(CH3)2 –O –]x, a member of the symmetrical dialkyl polysiloxanes, with repeat unit [SiR2 –O –]x. This polymer is discussed extensively in the following chapters, particularly in chapter 5. Other members of this series are poly(diethylsiloxane) [Si(C2H5) –O–]x, and poly(di-n-propylsiloxane) [SiC3H7)2–O–]x. An example of an aryl member of the symmetrically substituted series is poly(diphenylsiloxane), with repeat unit [Si(C6H5)2–O–]x. This polymer is unusual because of its very high melting point and the mesophase it exhibits. The closely related polymer, poly(phenyl/tolylsiloxane), has also been prepared and studied. The unsymmetrically substituted polysiloxanes have the repeat unit [SiRR’O–]x, and are exemplified by poly(methylphenylsiloxane) [Si(CH3) (C6H5) –O–]xand poly(methylhydrosiloxane) [Si(CH3)(H) –O–]x. In some cases, one of the side chains has been unusually long, for example C6H13, C16H33, and C18H37, including a branched side chain—CH(CH3– (CH2)m–CH3. Another example has methoxy-substituted aromatic fragments as one of the two side chains in the repeat unit. Such chains have stereochemical variability in analogy with the vinyl polymers such as polypropylene [CH(CH3) –CH2–]xand vinylidene polymers such as poly(methyl methacrylate) [C(CH3)(C = OOCH3) –CH2–]xOne can also introduce optically active groups as side chains, the simplest example being the secondary butyl group—CH(CH3)(C2H5). Another example involves redox-active dendritic wedges containing ferrocenyl and carbonylchromium moieties. Other substituents have included phenylethenyl groups, cyclic siloxane groups, and Cr-bound carbazole chromophores. In a reversal of roles, some polymers were prepared to have PDMS side chains on a poly(phenylacetylene) main chain. Siloxane-terminated solubilizing side chains are used to improve the properties of thin-film transistors. Silalkylene polymers have methylene groups replacing the oxygen atoms in the backbone. Poly(dimethylsilmethylene) is an example, [Si(CH3)2–CH2]x. A variation on this theme is to include aryl groups, for example, in poly(dimethyldiphenylsilylenemethylene) [Si(CH3)2CH2Si(C6H5)2]x. Other aryl substituents, specifically tolyl groups, have also been included as side chains. It is also possible to insert a silphenylene group [Si(CH3)2–C6H4–] into the backbone of the polysiloxane repeat unit to give [Si(CH3)2–C6H4– Si(CH3)2O–], in which the phenylene can be para or ortho or meta. A specific example is poly(tetramethyl-p-silphenylene-siloxane).
Physical review, May 1, 1995
We present measurements of the superBuid density and heat capacity of thin films of He adsorbed i... more We present measurements of the superBuid density and heat capacity of thin films of He adsorbed in aerogel glass. We find that the critical behavior of the super8uid density for films with transition temperatures between 50 mK and 1 K is similar to that seen for Alms adsorbed on Vycor. Power-law behavior is observed over at least one order of magnitude in reduced temperature with an exponent (= 0.63 + 0.03. This exponent is much smaller than the value 0.811 + 0.004 found when the pores were filled with helium. We also find that the exponent is unchanged by the addition of small amounts of He. These results are consistent with the existence of a correlation length that diverges at the superfluid transition. Unlike for full-pore He aerogel, the correlation length is long compared with all structural length scales throughout the superQuid density power-law regime, thus leading to the more bulklike critical behavior. The heat capacity of He films in aerogel shows no singularity like that seen for full-pore He aerogel or for thin films adsorbed in Vycor. We show that this result is consistent with the predictions of hyperuniversality given the long correlation lengths implied by the super8uid density measurements. T seen in the latter system does not appear. The contrast with the full-pore results is particularly strong in this case, since the heat capacity of full-pore He-aerogel is marked by a singularity at T, (Refs. 10-12) which has not been observed for full-pore He-Vycor. ' This paper will discuss the results on thin films of He adsorbed in aerogel in the context of full-pore aerogel as well as the Vycor measurements. We will therefore refer frequently to any one of four systems: full-pore aerogel, thin-film aerogel, full-pore Vycor, and thin-film Vycor. Our results for thin-film He-aerogel are consistent with the existence of a three dimensional correlation length (that diverges at the superHuid transition. The data allow for at least two tests of this interpretation, which we have adopted previously for the other three systems. First, we find that the fundamental length scale go for the correlation length is much larger for thin films in aerogel than for full-pore aerogel. This implies that the Harris criterion, which appears to fail for the full-pore case, is more likely to apply to thin films. The measured critical behavior of the films is indeed closer to that of pure He than that of full-pore aerogel, in agree
Macromolecules, 2016
Nanocasting is an emerging method to prepare organic polymers with regular, nanometer pores using... more Nanocasting is an emerging method to prepare organic polymers with regular, nanometer pores using inorganic templates. This report assesses the impact of imperfect template replication on the sorption properties of such polymer castings. Existing X-ray diffraction data show that substantial diffuse scattering exists in the small-angle region even though TEM images show near perfect lattices of uniform pores. To assess the origin of the diffuse scattering, the morphology of the phenol− formaldehyde foams (PFF) was investigated by small-angle X-ray scattering (SAXS). The observed diffuse scattering is attributed to interfacial roughness due to fractal structures. Such roughness has a profound impact on the sorption properties. Conventional pore-filling models, for example, overestimate protein sorption capacity. A mathematical framework is presented to calculate sorption properties based on observed morphological parameters. The formalism uses the surface fractal dimension determined by SAXS in conjunction with nitrogen adsorption isotherms to predict lysozyme sorption. The results are consistent with measured lysozyme loading.
Materials Technology, 1994
any agency thereof, nor any of their employees, nor any of their contractors, subcc,_tractors, or... more any agency thereof, nor any of their employees, nor any of their contractors, subcc,_tractors, or their employees, makes any warranty, expresb or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trad-name, trademark, manufacturer, or otherwise, does not necessarily constitute orimplyits endorsement, recommendation, orfavoring by the United StatesGovernment,any agencythereof or any of their contractors orsubcontractors. The viewsand opinions expressed herein do notnecessarily state or reflect thoseoftheUnitedStates Government, any agencythereof or anyoftheir contractors. Prin_d in the United States of America. This report has been reproduced directly from the best available copy.
Polysiloxanes are the most studied inorganic and semi-inorganic polymers because of their many me... more Polysiloxanes are the most studied inorganic and semi-inorganic polymers because of their many medical and commercial uses. The Si-O backbone endows polysiloxanes with intriguing properties: the strength of the Si-O bond imparts considerable thermal stability, and the nature of the bonding imparts low surface free energy. Prostheses, artificial organs, objects for facial reconstruction, vitreous substitutes in the eyes, and tubing take advantage of the stability and pliability of polysiloxanes. Artificial skin, contact lenses, and drug delivery systems utilize their high permeability. Such biomedical applications have led to biocompatibility studies on the interactions of polysiloxanes with proteins, and there has been interest in modifying these materials to improve their suitability for general biomedical application. Polysiloxanes examines novel aspects of polysiloxane science and engineering, including properties, work in progress, and important unsolved problems. The volume, wi...
Polymer, 2004
Two series of segmented polyurethanes having soft segment concentration of 50 and 70 wt%, and dif... more Two series of segmented polyurethanes having soft segment concentration of 50 and 70 wt%, and different concentrations of nanometerdiameter silica were prepared and tested. Atomic force microscopy revealed a strong effect of nanoparticles on the large-scale spherulitic morphology of the hard domains. Addition of silica suppresses fibril formation in spherulites. Filler particles were evenly distributed in the hard and soft phase. Nano-silica affected the melting point of the hard phase only at loadings .30 wt% silica. A single melting peak was observed at higher filler loadings. There is no clear effect of the filler on the glass transition of soft segments. Wide-angle X-ray diffraction showed decreasing crystallinity of the hard domains with increasing filler concentration in samples with 70 wt% soft segment. Ultra smallangle X-ray scattering confirms the existence of nanometer phase-separated domains in the unfilled sample. These domains are disrupted in the presence of nano-silica. The picture that emerges is that nano-silica suppresses short-scale phase separation of the hard and soft segments. Undoubtedly, the formation of fibrils on larger scales is related to short-scale segment segregation, so when the latter is suppressed by the presence of silica, fibril growth is also impeded.
Applied Spectroscopy, 2010
The 1H-nuclear magnetic resonance (NMR) chemical shifts of ethanol and water hydroxyl groups show... more The 1H-nuclear magnetic resonance (NMR) chemical shifts of ethanol and water hydroxyl groups show a pattern change at a critical ethanol concentration. Below the critical value (20 mol% at 400 Hz), only one hydroxyl peak appears due to fast proton exchange, whereas above the critical concentration, the ethanol hydroxyl peak splits from the water peak emerging as an individual chemical shift. The structural basis of the NMR pattern change was interpreted by a multivariate curve resolution–alternating least squares (MCR-ALS) analysis of the mid-infrared (mid-IR) spectra obtained for ethanol–water solutions. Results suggest that the NMR pattern change is due to the formation of ethanol–ethanol clusters. Below the critical concentration, no ethanol–ethanol clusters exist. Therefore, the NMR does not detect the ethanol environment. Above the critical ethanol concentration, ethanol–ethanol clusters first appear such that a distinct ethanol hydroxyl peak emerges. The basis for the dependen...
Journal of Agricultural and Food Chemistry, 2010
Although vodka is a reasonably pure mixture of alcohol and water, beverage drinks typically show ... more Although vodka is a reasonably pure mixture of alcohol and water, beverage drinks typically show differences in appeal among brands. The question immediately arises as to the molecular basis, if any, of vodka taste perception. This study shows that commercial vodkas differ measurably from ethanol-water solutions. Specifically, differences in hydrogen-bonding strength among vodkas are observed by 1 H NMR, FT-IR, and Raman spectroscopy. Component analysis of the FT-IR and Raman data reveals a water-rich hydrate of composition E 3 (5.3 (0.1)H 2 O prevalent in both vodka and water-ethanol solutions. This composition is close to that of a clathrate-hydrate observed at low temperature, implying a cage-like morphology. A structurability parameter (SP) is defined by the concentration of the E 3 (5.3 (0.1)H 2 O hydrate compared to pure ethanol-water at the same alcohol content. SP thus measures the deviation of vodka from "clean" ethanol-water solutions. SP quantifies the effect of a variety of trace compounds present in vodka. It is argued that the hydrate structure E 3 (5.3 (0.1)H 2 O and its content are related to the perception of vodka.
In most scattering experiments the scattered light field represents a chaotic superposition of fi... more In most scattering experiments the scattered light field represents a chaotic superposition of fields scattered from a large number of individual scatterers and therefore obeys Gaussian statistics [1]. That is, the amplitude distribution of the fluctuating scattered field is Gaussian. It is the purpose of this paper to investigate the single time-interval statistics of the scattered light when the number of scatterers is not large. Under these conditions the scattered field is not Gaussian.
MRS Proceedings, 1984
ABSTRACTSmall angle x-ray scattering (SAXS) is the technique of choice for the determination of s... more ABSTRACTSmall angle x-ray scattering (SAXS) is the technique of choice for the determination of structure on the 10–1000Å scale. We have used this technique to study the growth and topology of the macromolecules which precede gelation in several chemical systems used in sol-gel glass technology. The results show that branched polymers, as opposed to colloids, are formed. The alcoholic silica system is akin to organic systems where gelation occurs through growth and crosslinking of chain molecules. Data are reported from both the Porod and Guinier regions of the SAXS curve and these data are interpreted in terms of geometrical structures predicted by various disorderly growth processes. The results indicate that the degree of crosslinking can be controlled by catalytic conditions. The degree of crosslinking may, in turn, control phase separation and processability to a dense glass.
… Materials. Wiley, New …, 1992
Octadecylamine-modified graphene-oxide (OMGO) polybutadiene nanocomposites with different OMGO lo... more Octadecylamine-modified graphene-oxide (OMGO) polybutadiene nanocomposites with different OMGO loadings were prepared by solution mixing. The dispersion of OMGO in chloroform is greatly improved compared to GO. Toughness and elongation of PBD–OMGO nanocomposites increase by 332% and 191% respectively compared with pure PBD. However, Young's modulus of PBD–OMGO nanocomposite decreases by 10% at 2-wt% loading. Graphene sheet crumpling accounts for the increased toughness, the absence of modulus reinforcement and the absence of a Payne effect for PBD–OMGO. The oxidation susceptibility of PBD is greatly reduced after the addition of OMGO, which is particularly desirable in the tire industry.
Materials and Processing Report
This book discusses the development of polymeric materials over the last 30 years. The chemist&am... more This book discusses the development of polymeric materials over the last 30 years. The chemist's ability to manipulate structure and tailor the properties of organic materials for specific applications is presented. The phenomenal success of polymer chemistry is addressed. The need for a research base in multiphase polymeric materials similar to that which underlies single-phase organics is examined.
Journal of industrial microbiology & biotechnology, 2018
Pseudomonas aeruginosa is a metabolically voracious bacterium that is easily manipulated genetica... more Pseudomonas aeruginosa is a metabolically voracious bacterium that is easily manipulated genetically. We have previously shown that the organism is also highly electrogenic in microbial fuel cells (MFCs). Polarization studies were performed in MFCs with wild-type strain PAO1 and three mutant strains (pilT, bdlA and pilT bdlA). The pilT mutant was hyperpiliated, while the bdlA mutant was suppressed in biofilm dispersion chemotaxis. The double pilT bdlA mutant was expected to have properties of both mutations. Polarization data indicate that the pilT mutant showed 5.0- and 3.2-fold increases in peak power compared to the wild type and the pilT bdlA mutant, respectively. The performance of the bdlA mutant was surprisingly the lowest, while the pilT bdlA electrogenic performance fell between the pilT mutant and wild-type bacteria. Measurements of biofilm thickness and bacterial viability showed equal viability among the different strains. The thickness of the bdlA mutant, however, was t...
Langmuir : the ACS journal of surfaces and colloids, Jan 14, 2018
This work exploits gas adsorption and small-angle X-ray scattering (SAXS) to illuminate morpholog... more This work exploits gas adsorption and small-angle X-ray scattering (SAXS) to illuminate morphology of complex nanoporous materials. We resolve multiple classes of porosity including previously undetected large-scale texture that significantly compromises the canonical interpretation of gas adsorption. Specifically, a UVM-7 class mesoporous silica was synthesized that has morphological features on three length scales: macropores due to packing of 150-nm globules, 1.9-nm-radius spherical mesopores inside the globules and >7-nm pockets on and between the globules. The total and external surface areas, as well as the mesopore volume, were determined using gas adsorption (α-plot) and SAXS. A new approach was applied to the SAXS data using multi-level fitting to determine the surface areas on multiple length scales. The SAXS analysis code is applicable to any two-phase system and is freely available to the public. The total surface area determined by SAXS was 12% greater than that obta...
Journal of Physics A: Mathematical, Nuclear and General
ABSTRACT
AIP Conference Proceedings
Several porous silicas have been studied in order to detenrdne the origin of porosity in random p... more Several porous silicas have been studied in order to detenrdne the origin of porosity in random porQJS media. The silica system offers a unique opportunity to atudy the .origin d. porous stn.ict.ures because a variety of different stl"Uctures •can be BJ?lthe91%ed depending on precursor chemistry and physics. In solution-grown materials, tor example, it is possible to grow particles with randomly rough surfaces, snooth surfaces, as well as polymerlike structures. Porous materials can be made rran all these synthetic precursors and the structure of the final product reflects the geometry of the precursors. In addition, porous materials can be made by a phase-separation/leaching process which gives rise to a completely different type of porosity network. Structures rran these various classes have been studied by small-angle x-ray and neutron scattering and in some cases it is p~sible to directly trace the structure of the porous material to the geometry of the precursor macromolecules.
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Papers by Dale W. Schaefer