Papers by Kristoffer Almdal
Polymer Degradation and Stability, 2005
The influence of a commercial grade and a pure anionic surfactant (dodecylbenzenesulfonic acid so... more The influence of a commercial grade and a pure anionic surfactant (dodecylbenzenesulfonic acid sodium salt, DBS) in aqueous solutions on the environmental stress cracking (ESC) of high-density polyethylene (HDPE) has been investigated. Injection moulded HDPE samples in ''dog-bone'' shape were exposed to the aqueous solutions of surfactant (0.14 M) at 80 C under strain (3 Z 1.2%) for 5 days. Both the commercial and pure surfactants caused cracks under the experimental conditions. The change in surface chemistry of the HDPE was followed using attenuated total reflectance Fourier transform infrared (ATR-FTIR) and Raman spectroscopy. The thermogravimetric analysis (TGA) did not show any significant differences in thermal stability of the samples studied. Differential scanning calorimetry (DSC) analysis, however, revealed an increase in crystallinity of the exposed samples. Wide Angle X-ray Scattering (WAXS) indicated that the HDPE sample has a boundary of both preferred and random (isotropic) crystallite orientations close and far away from the injection moulding inlet, respectively. The structure of the surfactants in solution was investigated by light scattering (LS). This showed that the commercial grade surfactant forms large aggregates (e.g., 500 nm) both at room temperature and at the exposure temperature of 80 C, whereas the pure surfactant has a critical micelle temperature (CMT) of around 45 C. Below the CMT aggregates are formed, and above the CMT the surfactants are unimeric. Matrix-assisted laser desorption ionisation time-of-flight mass spectrometry (MALDI-TOF-MS) analysis revealed that the commercial surfactant has a wide distribution of hydrocarbon chains from C-10 to C-13, whereas the pure one contains predominantly hydrocarbon dodecyl (chain of C-12).
Soft Matter
By a selective complexation between different alkyltrimethylammonium amphiphiles (C8, C12 and C16... more By a selective complexation between different alkyltrimethylammonium amphiphiles (C8, C12 and C16) and three different diblock copolymer systems of poly(styrene)-b-poly(methacrylic acid) at various grafting densities X (X = number of alkyl chains per acidic group of the poly(methacrylic acid) PMAA block), a class of ionic supramolecules are successfully synthesized whose molecular architecture consists of a poly(styrene) PS block (Linear block) covalently connected to a strongly amphiphilic comb-like block (AmphComb block), i.e. Linear-b-AmphComb. In the melt state, these ionic supramolecules can show simultaneous microphase (between Linear and AmphComb blocks) and nanophase (within the AmphComb blocks) separations. This leads to the formation of various structure-in-structure two-scale hierarchical self-assemblies, including S-in-SLL, S-in-SBCC, S-in-C, S-in-L and C-in-L, where S, SLL, SBCC, C and L stand for spherical, spherical in liquid-like state, spherical in body-centered-cub...
Physica B: Condensed Matter, 1997
Thermal composition fluctuations in three diblock copolymers were studied with SANS as a function... more Thermal composition fluctuations in three diblock copolymers were studied with SANS as a function of temperature and pressure (0.1-200 MPa). In all cases the phase diagram shows an unusual shape insofar as with increasing pressure the order disorder temperature Top T first decreases and then increases. The pressure induced changes of Too x are caused by the increase of the enthalpic and entropic terms of the Flory-Huggins parameter. (t;) 1998 Elsevier Science B.V. All rights reserved.
Journal de Physique II, 1997
Il Nuovo Cimento D, 1994
Summary A homologous series of nine symmetric poly(styrene)-block-poly(butadieme) diblock copoly... more Summary A homologous series of nine symmetric poly(styrene)-block-poly(butadieme) diblock copolymers was synthesized and characterized. The scaling of the lamellar thickness,D, with the chain lengthN(DαN δ ) was investigated with small-angle X-ray scattering. Different sample preparation methods were used: annealing, solvent-casting and shear alignment. We find that the lamellar thickness and thus the value of the exponent δ depends on the preparation method used,i.e. care must be taken to ensure that the samples investigated are in thermodynamic equilibrium.
Journal de Physique II, 1996
Journal de Physique II, 1994
Uploads
Papers by Kristoffer Almdal