Structure of swollen polydimethyl siloxane gels

Mallam, Simon; Hecht, Anne‐Marie; Geissler, Erik; Pruvost, Pierre

doi:10.1063/1.457412

Cited by 67 publications

(51 citation statements)

References 10 publications

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“…18 , 27 The former were made by cross linking in solution. The average number of monomer units between neighboring cross links (cross linker glutaraldehyde) was varied between 50 and 400.…”

Section: Methodsmentioning

confidence: 99%

Structure and thermodynamics of flexible polymer gels

Geissler

Horkay

Hecht

1994

The Journal of Chemical Physics

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Unlike the situation for polymer solutions, for swollen polymer networks, there is no generally accepted relation between the macroscopic osmotic properties and the scattering behavior. Complementary measurements involving osmotic and elastic observations, small angle neutron and x-ray scattering, as well as quasielastic light scattering, can, however, yield detailed information on the relationship between the structure and the thermodynamics in polymer gels. Here, we apply such a complementary investigation to two types of networks, differing in the mechanism of cross linking. The neutron scattering spectra of the gels contain two components, dynamic and static. The former is governed by the macroscopic osmotic and elastic moduli of the swollen network, and is associated with the thermodynamic concentration fluctuations. The static component of the scattered intensity is generated by local variations of the cross-link density. The amplitude of the static concentration fluctuations 〈δφ2〉/φ2 is determined by the detailed mechanism of the cross-linking procedure. Its concentration dependence can be expressed in terms of the same macroscopic osmotic and elastic variables as govern the thermodynamic properties of the gel.

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“…18 , 27 The former were made by cross linking in solution. The average number of monomer units between neighboring cross links (cross linker glutaraldehyde) was varied between 50 and 400.…”

Section: Methodsmentioning

confidence: 99%

Structure and thermodynamics of flexible polymer gels

Geissler

Horkay

Hecht

1994

The Journal of Chemical Physics

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“…positioned randomly, they can be described by a Gaussian with a characteristic length ∆R, and we obtain 52 It is implicitly assumed in eq 14 that polymer concentration fluctuations are decoupled from hydrophobe density fluctuations, 53 i.e., the two order parameters are independent. Figure 11 shows fits to the SAXS curves obtained for 5DPAM1.1 and 3DPAM1.1 solutions using eqs 13 and 14, respectively.…”

Section: Small-angle X-raymentioning

confidence: 99%

Rheological and Structural Characterization of Hydrophobically Modified Polyacrylamide Solutions in the Semidilute Regime

et al. 2004

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Semidilute solutions of two series of polyacrylamide (AM)-based copolymers containing hydrophobic di-n-propylacrylamide (DPAM) and di-n-octylacrylamide (DOAM) comonomers, namely P(DPAM-co-AM) and P(DOAM-co-AM), have been characterized using rheology and small angle X-ray scattering (SAXS). The relaxation time and plateau modulus obtained from rheology, and the correlation length ( ) obtained from SAXS are compared for copolymers with different hydrophobe content (f) and hydrophobe block length (N H). Shear rheometry experiments revealed that P(DOAM-co-AM) copolymers formed gels characterized by a broad distribution of relaxation modes. In contrast, solutions of P(DPAMco-AM) copolymers exhibited a near-Maxwellian response although additional fast modes contribute significantly to the dynamic shear modulus at high frequency. For both copolymers, the dynamic shear moduli obtained at different temperatures could be time-temperature superposed, with a shift factor described by the Williams-Landel-Ferry equation. For P(DPAM-co-AM) solutions, the sticker lifetime (determined from the fitting of the dynamic moduli to a Maxwell model) was found to increase with increasing f but to be insensitive to N H, in the range examined. However, the plateau modulus Go decreases with increasing NH, which is related to the increase in strand length between stickers. Similar to P(DPAMco-AM) solutions, one relaxation time for the gels of copolymers with longer hydrophobes (in this case determined from the crossover in the elastic moduli) is more sensitive to f than to NH. The SAXS data for the P(DPAM-co-AM) solutions could be modeled using the structure factor for a polymer solution in a good solvent although enhanced fluctuations had to be considered for the polymers with higher hydrophobe content. The correlation length was found to decrease with increasing temperature for P(DPAM-co-AM) solutions, due an improvement of the solvent quality. But did not depend on the temperature for P(DOAM-co-AM) samples, probably due to stronger associations between hydrophobes. Trends of with N H and f are discussed.

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“…where (8ip 2 )d is the mean square amplitude of the thermodynamic fluctuations of <p. It is found [2,3,11,12] that I<j(Q) corresponding to {8<p 2 )d can be represented in the low Q region by an Ornstein-Zernike function [13,14] …”

mentioning

confidence: 98%

“…We have found [2,3] that the scattering spectra of swollen gels can be treated as the sum of two separate components, a static and a dynamic scattering function I S (Q) and /</((? ), respectively.…”

mentioning

confidence: 99%