A generalized Flory-Huggins theory for use in fitting and predicting liquid-liquid phase diagrams is presented. The parameter is defined through the chemical potential of the diluent and is represented as a product of composition-dependent and temperature-dependent terms. The former is quadratic, and the latter contains a logarithmic term in addition to the usual linear dependence on 1/T. The Koningsveld g factor is obtained by integration of the composition-dependent . Comparisons are made with experimental data, and it is shown that the functional form that is chosen for is sufficient to fit phase diagrams having a upper and lower critical solution temperatures, combination of the two with the LCST lying above the UCST, closed loop, and hourglass shapes. Such comparisons may be used to extract the temperature and concentration dependence of for the system. Both binodals and spinodals are calculated. The treatment is applicable to polymer blends as well as solutions with low molecular weight diluents.

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We study conformational properties of the polyelectrolyte chain with prescribed Bernoullian distribution of positive and negative charges on its backbone. For the case when the total charge of the chain is almost zero, the charge fluctuations are of special importance leading to the collapse transition qualitatively different from that expected for the uncharged homopolymers. The present case of collapse transition directly demonstrates the biological significance of nonuniformly charged polymers.

This study shows that the structure of the poly(diphenylsiloxane) (PDPhS) backbone is quasi-planar rather than helical. The nearest-neighbor chains in the crystal are packed in a hexagonal configuration. Using molecular mechanics calculations and analysis of X-ray powder diffraction data, it has been determined that the crystalline structure of PDPhS has Pbn2\ symmetry and the backbone consists of siloxane bonds in a quasi cis-trans sequential conformation. The deviation of each bond from the planar configuration is about 15°. The backbones of the two chains in the unit cell are antisymmetrical. The Si-O-Si bond angle is 145°and the torsional angles of the vicinal phenyl groups relative to each other are 125 and 72°. The orientation of the phenyl groups in the crystal consists of parallel and perpendicular nearest neighbors. The calculated X-ray results are able to explain the main features of the experimental pattern in terms of position and intensity of the peaks. Molecular mechanics calculations suggest that the density of ideal crystals of poly(diphenylsiloxane) at low temperatures should be in the range 1.26-1.3 g/cm3, whereas the reported experimental value is 1.22 g/cm3. A new set of molecular mechanics parameters for the UFF method to more accurately describe polysiloxanes in the condensed state is given.

The global textile industry has an ongoing need for improved softening products. Current materials systems, including those with siloxane polymers, exhibit certain limitations such as yellowing, high cost, and low softening efficiency. Investigations into fabric softening mechanisms invoke molecular modeling tools to simulate siloxane polymer and cotton fiber interactions at the molecular level. This research describes how certain polymer types exhibit fundamentally enhanced siloxane and fiber interactions within particular pH ranges. Molecular modeling results are also correlated with empirical findings. The output of this research adds insight into efforts to understand fabric softening phenomena.Siloxanes have low surface energy, excellent lubricity, heat stability, and limited solubility in organics, coupled with water insolubility. At the molecular level, the fabric softening properties of siloxanes are believed to be derived from the flexibility of the siloxane backbone [ 12] that results from the freedom of rotations about the Si--O-Si linkages and the low interaction energies of the methyl groups. At room temperature, there is virtually no energy barrier to prevent molecular flexing [ 12,13]. Consequently, siloxanes act as highly effective lubricants in reducing fiber-on-fiber friction. Siloxane functional groups provide strong attractive interactions between the fabric softener and the cotton surface, without which the softener would wash off over time.To enhance interactions between siloxanes and textile materials to increase durability during processes such as washing, reactive siloxanes and modified, nonfunctional siloxane structures are used [ 19]. Indeed, modifying nonfunctional siloxane structures by replacing pendant or terminal methyl groups with various organic functional groups brings a wide range of physical properties to the siloxane polymers. Amino functional groups play an important role in providing enhanced softening properties to organosilicone compounds [8]. In practice, amino functional silicones are widely used in the textile industry as premium-grade fabric softeners [9, 18, 1].Because of the interactions of amino groups with textile materials, amino functional siloxanes are physically adsorbed onto fiber surfaces. This adsorption feature improves the durability of amino functional siloxane fabric softeners during the washing process. The amino groups become cationic (-NH3+) at acidic conditions, and the ionization provides strong attractions to the fabric. The physical properties of typical aminoalkyl functional siloxanes have been described in detail in the literature [ 17]. The objective of this work is to gain a better understanding of the basic softening phenomena of aminoalkyl functional siloxanes on cotton fabrics. Specifically, this report discusses the effect of pH on softening efficiency derived from aminoalkyl functional siloxanes. Molecular modeling results relate experimental observations with chemical and intermolecular interactions to study the softening mechanism.