Measurement of molecular dimensions of polystyrene chains in the bulk polymer by low angle neutron diffraction

Ballard, D. G. H.; Wignall, G. D.; Schelten, J.

doi:10.1016/0014-3057(73)90059-1

Cited by 245 publications

(81 citation statements)

References 9 publications

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“…Taking into account the scatter in a, however, there is no distinct molecular weight dependence of a. This length scale is of the same order as that of the statistical segment of polystyrene (0.68nm) [32]. These experimental results for T ∞ g and a suggest that the thickness dependence of T g is almost independent of the molecular weight of a-PS after rescaling with respect to T g of bulk samples.…”

Section: Glass Transition Temperature Of Thin Filmssupporting

confidence: 60%

Glass transitions and dynamics in thin polymer films: Dielectric relaxation of thin films of polystyrene

2000

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The glass transition temperature Tg and the temperature Tα corresponding to the peak in the dielectric loss due to the α-process have been simultaneously determined as functions of film thickness d through dielectric measurements for polystyrene thin films supported on glass substrate. The dielectric loss peaks have also been investigated as functions of frequency for a given temperature. A decrease in Tg was observed with decreasing film thickness, while Tα was found to remain almost constant for d > dc and to decrease drastically with decreasing d for d < dc. Here, dc is a critical thickness dependent on molecular weight. The relaxation time τα of the α-process, which was measured as the frequency at which the dielectric loss realizes its peak value at a given temperature, was found to have a d dependence similar to that of Tα. The relaxation function for the α-process was obtained by using the observed frequency dependence of the peak profile of the dielectric loss. The exponent βKWW, which was obtained from the relaxation functions, decreases as thickness decreases. This suggests that the distribution of relaxation times for the α-process broadens with decreasing thickness. The thickness dependence of Tg is directly related to the distribution of relaxation times for the α-process, not to the relaxation time itself. The value of the thermal expansion coefficient normal to the film surface was found to increase with decreasing film thickness below Tg, but to decrease with decreasing film thickness above Tg. These experimental results are discussed in the context of a three-layer model in which within thin films there are three layers with different mobilities and glass transition temperatures.

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Section: Glass Transition Temperature Of Thin Filmssupporting

confidence: 60%

Glass transitions and dynamics in thin polymer films: Dielectric relaxation of thin films of polystyrene

2000

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“…They are PEOX (MW ) 50 000 and MW ) 500 000) solutions with concentration of 1 mg/mL in methanol, PEOX (MW ) 500 000) with concentration of 0.5 mg/mL, and PEOX-PEI copolymer solution (concentration ) 1 mg/mL, MW ) 500 000). Previous research has indicated that both the molecular weight of the polymer 32 and the concentration of the polymer solution 22 in spincoating influence the outcome of the experiment significantly. The ellipsometric results from our study showed that reducing the MW of the polymer and lowering the concentration of the polymer solution both decrease the final dry thickness of the polymer layer.…”

Section: Resultsmentioning

confidence: 99%

Polymer-Supported Lipid Bilayers on Benzophenone-Modified Substrates

et al. 2000

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Solid-supported lipid membranes are important for their roles in fundamental biophysical research as well as in applications such as biosensors. In our study, lipopolymers containing alkyl side chains were synthesized and a mixture of the lipopolymer and free lipids was preorganized at the air-water interface and then transferred to a solid substrate using the Langmuir-Blodgett technique. A photochemical reaction between a substrate-functionalized benzophenone and C-H bonds on the lipopolymer was used to attach the lipopolymers to the substrate. The final assembly of the membrane was completed by vesicle fusion. Langmuir film experiments at the air-water interface indicate tighter molecular packing for the lipopolymers with 28 mol % alkyl side chains than for the ones with 22 mol %. Atomic force microscopy images point to phase separation of lipopolymers on the substrates due to their dewetting from hydrophobic surfaces. However, a mixture of lipopolymers and free lipids formed a smooth film on the same substrate. After the addition of the second lipid layer on the lipopolymer/free lipid layer, the fluorescence images of the polymer-supported bilayer suggested that the distal lipid layer is homogeneous on the micrometer scale. The relaxation of the fluorescent probe lipids was analyzed after application of an electric field to determine their diffusion coefficient; the distal lipid layer was mobile with an average diffusion coefficient of ∼0.1 µm 2 /s. Moreover, the immobile fraction of the lipids in the distal layer was estimated to be around 15%.

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“…Recently, <S 2 ) for the polymer with single side group has been studied. s-io The calculated values of <S 2 ) for polyethylene (PE) and polypropylene (PP) with considering side groups (C-H) and (C-CH 3 ) are more approched to the experimental data. In this paper, the mean-square radius of gyration of polymer chains with two side groups, which have the different geometric structures and the heavier group masses, are investigated by using the RIS theory, and the expression for <S 2 ) may be apply to 1,2-polybutadiene (1,2-PBD), PP, polydimethylsiloxane (PDMS), and other monsubstituted polymers.…”

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confidence: 97%