The role of short chain molecules for the rheology of polystyrene melts.

Knoglinger, H.; Schausberger, A.; Janeschitz‐Kriegl, H.

doi:10.1007/bf01333847

Cited by 8 publications

(7 citation statements)

References 30 publications

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“…The question of how a smaller additive will influence the behaviour of a larger molecule is also pertinent in polymer literature [39]. The finding that short chains lower the stress response of long chains is often observed in bulk polymer rsif.royalsocietypublishing.org J R Soc Interface 10: 20120987 systems.…”

Section: Influence Of Molecule Length On Interfacial Rheologymentioning

confidence: 99%

Insights into the role of protein molecule size and structure on interfacial properties using designed sequences

Dwyer

James

et al. 2013

J. R. Soc. Interface.

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Mixtures of a large, structured protein with a smaller, unstructured component are inherently complex and hard to characterize at interfaces, leading to difficulties in understanding their interfacial behaviours and, therefore, formulation optimization. Here, we investigated interfacial properties of such a mixed system. Simplicity was achieved using designed sequences in which chemical differences had been eliminated to isolate the effect of molecular size and structure, namely a short unstructured peptide (DAMP1) and its longer structured protein concatamer (DAMP4). Interfacial tension measurements suggested that the size and bulk structuring of the larger molecule led to much slower adsorption kinetics. Neutron reflectometry at equilibrium revealed that both molecules adsorbed as a monolayer to the air -water interface (indicating unfolding of DAMP4 to give a chain of four connected DAMP1 molecules), with a concentration ratio equal to that in the bulk. This suggests the overall free energy of adsorption is equal despite differences in size and bulk structure. At small interfacial extensional strains, only molecule packing influenced the stress response. At larger strains, the effect of size became apparent, with DAMP4 registering a higher stress response and interfacial elasticity. When both components were present at the interface, most stress-dissipating movement was achieved by DAMP1. This work thus provides insights into the role of proteins' molecular size and structure on their interfacial properties, and the designed sequences introduced here can serve as effective tools for interfacial studies of proteins and polymers.

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Section: Influence Of Molecule Length On Interfacial Rheologymentioning

confidence: 99%

Insights into the role of protein molecule size and structure on interfacial properties using designed sequences

Dwyer

James

et al. 2013

J. R. Soc. Interface.

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“…The preparation procedure of the mixtures and the measurements have been described in detail in a previous paper [11]. The moduli were measured at different temperatures (150, 160, 180 and 200 °C) and reduced to 180 °C with the aid of the time-temperature superposition principle as reported in [14].…”

Section: Resultsmentioning

confidence: 99%

“…This factor K is, as has been shown in more detail in [14], proportional to exp [B/(fo + A/M,)], where M, is the number average molar mass [kg/mol] whereas B = 0.535, f0 = 0.046 and A = 0.034 kg/mol are specific parameters for polystyrene at a temperature of 180 °C. As the influence of the ends vanishes for very long molecules [ lim K = Koo = 11 the molar-mass-depen\Ms -* oo ] dent factor K is normalized by the following equation:…”

Section: Relaxation Timesmentioning

confidence: 96%

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The role of short chain molecules for the rheology of polystyrene melts.

1987

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Abstract." The influence of short chain molecules (with M < M c ) on the rheology of the melts of binary blends of long and short chain polymers was studied. For this purpose, the complex moduli as functions of circular frequency were examined for these melts and also for melts of unblended long chain samples. For pertinent blending a set of standard polystyrenes with narrow molar mass distribution was used.The short chain component causes a typical diluent effect. This is clearly revealed from the lowering of the plateau modulus of the long chain component. This lowering is found to be proportional to the square of the weight fraction w2 of the long chain component, as theoretically predicted. The reduction of the relaxation times of the long chain molecules turns out to be proportional to w~ '8, when the influence of an increased contribution of chain ends to the free volume is separately taken into account according to the results of the first paper of this series. As the power of w2 in the latter relation is not critical, one can formulate equations for the first normal-stress coefficient and for the zero-shear viscosity as functions of w2M~.~, which merge into the respective M 6'8-and M34-1aws well-established for undiluted high polymers (w2 = 1).

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“…The two polymers are fairly narrow in their molecular weight distribution but not narrow enough to exhibit the distinct bimodal mode distribution of binary blends. [20,21] The relaxation processes of the two polymers are too broadly distributed to be distinguished individually when blending the two polymers. l iPP302 /l iPP140 is about 232 (see Table 2), which corresponds to an M w ratio of about 5.3.…”

Section: Discussionmentioning

confidence: 99%

Isotactic Poly(propylene) Crystallization: Role of Small Fractions of High or Low Molecular Weight Polymer

Elmoumni

Gonzalez-Ruiz

Coughlin

et al. 2004

Macro Chemistry & Physics

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Summary: Two well‐characterized metallocene isotactic poly(propylene) (iPP) samples, one of high and one of low molecular weight, were blended together for studying the effects of a second component on quiescent and shear‐induced crystallization. A small amount of added high molecular weight (HMW) (up to 10 wt.‐%) polymer increases the quiescent crystallization rate. This was observed as a decrease in characteristic halftime of transmitted light intensity. The crystallization halftime increases again when adding more than 10 wt.‐% of HMW polymer. The crystallization halftime of pre‐sheared samples decreases with increasing HMW fraction and is lowest for the HMW sample by itself. For the specific shearing conditions (γ = 600, Tx = 145 °C), wide‐angle X‐ray diffraction (WAXD) images show the presence of the gamma (γ) crystalline phase of iPP for samples containing 25 wt.‐% of HMW and higher. DSC thermograms demonstrated higher crystalline fractions with increasing HMW fraction in pre‐sheared samples.Optical micrograph of an iPP sample after quiescent crystallization at 145 °C.magnified imageOptical micrograph of an iPP sample after quiescent crystallization at 145 °C.

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The role of short chain molecules for the rheology of polystyrene melts.

Cited by 8 publications

References 30 publications

Insights into the role of protein molecule size and structure on interfacial properties using designed sequences

Insights into the role of protein molecule size and structure on interfacial properties using designed sequences

The role of short chain molecules for the rheology of polystyrene melts.

Isotactic Poly(propylene) Crystallization: Role of Small Fractions of High or Low Molecular Weight Polymer

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