Anomalous freezing point depression of swollen gels

Boonstra, Beitske; Heckman, F. A.; Taylor, G. L.

doi:10.1002/app.1968.070120201

Cited by 32 publications

(28 citation statements)

References 13 publications

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“…It was shown that the smaller the mesh size, the smaller the crystal size and the lower the observed freezing point. This agrees with the results of Boonstra et al, 13 Oikawa and Murakami, 14 and Honiball et al, 16 where a more tightly crosslinked network (i.e., one with a smaller mesh size) produced a larger depression in the freezing point of the solvent. However, these workers determined that the freezing point depression was too large to have been caused solely by a reduction in crystal size.…”

Section: Introductionsupporting

confidence: 92%

“…Many researchers [13][14][15][16][17] have investigated the interaction between a solvent and a rubbery polymer by studying the freezing and melting behavior of the solvent. It has been observed 13,14,16 that the higher the volume fraction of rubber in solvent/rubber mixtures, the lower the freezing point of the solvent.…”

Section: Introductionmentioning

confidence: 99%

“…It has been observed 13,14,16 that the higher the volume fraction of rubber in solvent/rubber mixtures, the lower the freezing point of the solvent. This phenomenon was described by Khun et al, 15 who proposed that the freezing point depression of solvents in solvent/ rubber mixtures or gels is related to the "mesh size" of the swollen network strands of the polymer in the gel.…”

Section: Introductionmentioning

confidence: 99%

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Thermal behavior of core-shell rubber/styrene monomer gels

Roberts

Simon

Cook

et al. 2000

J. Polym. Sci. B Polym. Phys.

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Section: Introductionsupporting

confidence: 92%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Thermal behavior of core-shell rubber/styrene monomer gels

Roberts

Simon

Cook

et al. 2000

J. Polym. Sci. B Polym. Phys.

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“…[19][20][21][22] Honiball et al 20 suggested that it was the difficulty in nucleation of the solvent which lead to the excess DT f . Using X-ray measurements to study the crystal size of benzene, Boonstra et al 21 concluded that there was no significant difference of crystal size in uncrosslinked and crosslinked rubbers. This work, however, was found to be inconclusive by Jackson and McKenna.…”

Section: Introductionmentioning

confidence: 99%

Anomalous melting behavior of cyclohexane and cyclooctane in poly(dimethyl siloxane) precursors and model networks

McKenna

2008

J Polym Sci B Polym Phys

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Building on previous observations of anomalous melting behavior of solvents in polyisoprene, we have expanded our insight into the melting behavior of organic solvents in polymers and polymer networks through a calorimetric investigation of cylcohexane and cyclooctane in poly(dimethyl siloxane) (PDMS) precursors and model networks. The results are contrary to general expectations. Besides deviations between the predictions of the Flory-Huggins model and observed melting point depression of the small molecule organics, it is found that the melting point depression of cyclohexane in model networks is lower than that in the uncrosslinked precursors and unaffected by the molecular weight between crosslinks, which is not consistent with the general observation that higher crosslinking density leads to greater melting point depression. We interpret the observed phenomenon in terms of phase separation. In the case of cyclooctane, it exhibits a double melting peak in the model networks with high molecular weight between crosslinks. Furthermore, the heats of fusion of both cyclohexane and cyclooctane decrease with increasing polymer volume fraction which violates the underlying assumption that the heat of fusion of solvent in the polymer is the same as that in the bulk for both the Flory-Huggins model and the Gibbs-Thomson equation.

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“…This anomalous freezing-point depression has been widely described by various authors. [13][14][15][16][17] Kuhn and Majer [13] attributed this anomaly to limited crystal growth in the gel, resulting from a mesh formed by chain segments in the polymer network. Hence, a higher vapor pressure can be expected for microcrystals because of their high surface to volume ratio, rendering a decrease in their freezing point.…”

Section: Introductionmentioning

confidence: 99%

Novel Approach of Evaluating Polymer Nanocomposite Structure by Measurements of the Freezing‐Point Depression

López–Manchado

Valentín

Herrero

et al. 2004

Macromol. Rapid Commun.

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IntroductionIn recent years, polymer/layered silicate (PLS) nanocomposites have attracted great interest, both in industry and in academia, because they exhibit unique properties not shared by their micro counterparts or conventional filled polymers. [1][2][3][4][5] The addition of just a few weight percent (<5 wt.-%) of nanolayered inorganic material gives rise to sensible increases in the stiffness and strength with minimal loss of ductility and impact resistance, [6,7] decreased gas permeability [8,9] and flammability, [10] improved abrasion and heat resistance, [11] and increased biodegradability of biodegradable polymers. [12] The physical mixture of a polymer and a layered silicate not necessarily gives rise to a nanocomposite. Depending on interfacial interactions between the polymer and layered silicates, three types of morphologies can occur: immiscible, intercalated, and exfoliated.The improved properties are only achieved when an exfoliated nanocomposite is formed. For this reason, it is very important to characterize the polymer nanocomposite structure prior to the analysis of their properties. The structure of the nanocomposites has typically been established by means of X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. Because of their easiness and availability, X-rays are most commonly used to determine the nanocomposite structure. However, one needs to be very careful with the interpretation of the results. Lack of sensibility in the analysis and limits of the equipment can lead to wrong conclusions about the nanocomposite structure. That is, the nanocomposites generally contain a fairly small amount of clay (less than 10 wt.-%), therefore the XRD analysis must be sensitive enough to detect the crystalline structure of the clay in the polymer. If this is not the case, no peaks appear in the diffraction pattern and a false conclusion, that a delaminated nanocomposite has been synthesized, might be drawn. Moreover, the analysis is Summary: A novel experimental approach based on the freezing-point depression of a solvent in a swollen gel has been developed to characterize the structure of nanocomposites. A higher depression in the freezing point has been related with an exfoliated nanocomposite. This increased depression not only depends on the formation of a tighter network but also on the decrease of the size of the solvent cages where the nucleation takes place.The nucleation process of unfilled and organoclay-filled natural rubber with the same crosslinking density.Communication 1309 performed at low angles in order to detect the (001) reflection and evaluate the spacing between the clay layers. It means that the irradiated surface may include not only the sample but also the sample holder. This might create a large amount of noise and, as a consequence, complicate the interpretation of the XRD patterns. Therefore, TEM is a necessary complement to confirm results obtained by XRD about the organization of the clay layers in the nanocomposite. TEM allows a qualitative u...

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Anomalous freezing point depression of swollen gels

Cited by 32 publications

References 13 publications

Thermal behavior of core-shell rubber/styrene monomer gels

Thermal behavior of core-shell rubber/styrene monomer gels

Anomalous melting behavior of cyclohexane and cyclooctane in poly(dimethyl siloxane) precursors and model networks

Novel Approach of Evaluating Polymer Nanocomposite Structure by Measurements of the Freezing‐Point Depression

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