Phase behavior of the polymer/drug system PLA/DEET: Effect of PLA molar mass on subambient liquid-liquid phase separation

Sungkapreecha, Chanita; Beily, Mark J.; Kreßler, Jörg; Focke, Walter Wilhelm; Androsch, René

doi:10.1016/j.tca.2017.12.021

Cited by 24 publications

(26 citation statements)

References 38 publications

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“…This result leads to the conclusion that at identical supercooling of the crystallizable component its mobility is increasing with the DEET concentration, perhaps contributing to the higher crystallization rate manifested with Figure . The above discussion notwithstanding, it may however be noted that at PLLA concentrations lower than about 40 m%, on suppression of crystallization, as can be achieved by fast cooling, vitrification of the solution is preceded by L‐L demixing …”

Section: Resultsmentioning

confidence: 91%

“…Here T m and

T_{m}^{0}

(= 200°C) are the equilibrium melting temperatures of PLLA crystals in the presence and absence of the solvent, respectively, R is the gas constant, ΔH u (= 10.76 kJ/mol) is the bulk enthalpy of melting of α‐crystals at

T_{m}^{0}

, and V u / V d (= 0.3) and ϕ d are the ratio of molar volumes of the polymer repeat unit and the diluent, and the volume‐based diluent concentration, respectively. The molar volumes of the polymer repeat unit and of the solvent were calculated by dividing their molar masses with the respective room‐temperature densities and assuming identical thermal expansion coefficients.…”

Section: Resultsmentioning

confidence: 99%

“…The strength of the enthalpic interaction between the polymer and the diluent is quantified with the Flory‐Huggins interaction parameter χ . For estimation of the equilibrium‐melting‐depression we used a χ ‐value of 0.33, based on a recent investigation of the temperature‐dependence of the PLLA/DEET phase behavior, allowing its extrapolation to the temperature of interest; the value of 0.33 is assumed being valid at

T_{m}^{0}

. Note that we are aware that there are reported numerous different values of equilibrium melting temperatures and bulk specific enthalpies of melting of PLLA in the literature .…”

Section: Resultsmentioning

confidence: 99%

“…Inspection of the final morphology of samples of different composition and crystallization history reveals at least qualitatively that the remaining liquid phase can be located rather inside the spherulites (see top left image) but also to a large fraction outside the spherulites, in particular when crystallization occurred at high temperature when the nucleation rate is low (see right‐column images). We assume that the composition of the remained liquid phase, which at the temperature of crystallization is well above both T g (see Figure ) and the L‐L phase separation temperature, is locally largely different; within spherulites, between crystal lamellae, the DEET‐content may be much lower than in interspherulitic regions, due to polymer depletion of the solution near the crystals.…”

Section: Resultsmentioning

confidence: 99%

“…We used N , N ‐diethyl‐3‐methylbenzamide (DEET) as a solvent, which is a well‐known mosquito repellent, and serving therefore not only as a solvent but also a drug with a specific functionality . The phase behavior of the particular system PLLA/DEET has been established in companion studies, revealing UCST behavior and S‐L type TIPS on cooling, being prerequisites for the study of the solution‐crystallization behavior. In a wider view, besides providing information about the control of the morphology of solution‐crystallized PLLA, research results may be compiled to rates of evaporation of the phase‐separated drug‐rich liquid phase, allowing tailoring its efficacy in repelling mosquitoes.…”

Section: Introductionmentioning

confidence: 99%

See 4 more Smart Citations

Crystallization of poly( l ‐lactic acid) in solution with the mosquito‐repellent N , N ‐diethyl‐3‐methylbenzamide

Sungkapreecha

Iqbal

Focke

et al. 2019

Polymer Crystallization

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Poly(l‐lactic acid) (PLLA) can be used as a carrier for the mosquito repellent N,N‐diethyl‐3‐methylbenzamide (DEET). PLLA dissolves in DEET at elevated temperature and crystallizes on cooling to below the concentration‐dependent equilibrium melting temperature, leading to scaffold formation. In this work, non‐isothermal and isothermal crystallization experiments were performed, using differential scanning calorimetry and polarized‐light optical microscopy. Crystallization of PLLA in solution with DEET is faster than melt‐crystallization of neat PLLA, with the maximum crystallization rate decreasing with decreasing PLLA content in the investigated range from 5 to 50 m% PLLA. The decrease of the maximum crystallization rate with increasing solvent content is due to decreases in both the maximum crystal growth rate and the nuclei density. The observed downward shift of the temperature range of crystallization is caused by the depression of equilibrium melting temperature and a strong decrease of the glass transition temperature, both occurring with increasing solvent concentration. It is assumed that the strong decrease of the glass transition temperature due to the presence of DEET, and the related increase of the mobility of PLLA chains, is the main reason for the increased crystallization rate compared to melt‐crystallization of PLLA. It is demonstrated that a large variety of spherulitic superstructures can be obtained by variation of the crystallization conditions, presumably leading to largely different 3D scaffold structures and DEET‐delivery characteristics.

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Section: Resultsmentioning

confidence: 91%

“…Here T m and

T_{m}^{0}

T_{m}^{0}

Section: Resultsmentioning

confidence: 99%

T_{m}^{0}

. Note that we are aware that there are reported numerous different values of equilibrium melting temperatures and bulk specific enthalpies of melting of PLLA in the literature .…”

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Crystallization of poly( l ‐lactic acid) in solution with the mosquito‐repellent N , N ‐diethyl‐3‐methylbenzamide

Sungkapreecha

Iqbal

Focke

et al. 2019

Polymer Crystallization

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Bulk Enthalpy of Melting of Poly (l‐lactic acid) (PLLA) Determined by Fast Scanning Chip Calorimetry

Jariyavidyanont

et al. 2022

Macromol. Rapid Commun.

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The bulk enthalpy of melting of 𝜶-crystals of poly (L-lactic acid) (PLLA) is evaluated by fast scanning calorimetry (FSC), by correlating the melting enthalpy of samples of different crystallinity with the corresponding heat capacity at 90 °C, that is at a temperature higher than the glass transition temperature of the bulk amorphous phase and lower than the melting temperature. Extrapolation of this relationship for crystals formed at 140 °C towards the heat capacity of fully solid PLLA yields a value of 104.5±6 J g −1 when melting occurs at 180-200 °C. The analysis relies on a two-phase structure, that is, absence of a vitrified rigid amorphous fraction (RAF) at the temperature of analysis the solid fraction (90 °C). Formation and vitrification of an RAF are suppressed by avoiding continuation of primary crystallization and secondary crystallization during cooling the system from the crystallization temperature of 140 °C to 90 °C, making use of the high cooling capacity of FSC. Small-angle X-ray scattering (SAXS) confirmed thickening of initially grown lamellae which only is possible if these lamellae are not surrounded by a glassy RAF. Linear crystallinity values obtained by SAXS and calorimetrically determined enthalpy-based crystallinities agree close to each other.

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A review on thermally induced phase separation technology in the fabrication of microporous polymer membrane devices for sustained‐repellent delivery: Crystallization and morphological studies

Mapossa,

Tewo,

Ray

et al. 2024

Journal of Polymer Science

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This article reports recent advances in thermally induced phase separation technology in fabricating microporous scaffold polymeric membranes as devices suitable for the controlled release of insect repellent. The key aspects, such as the crystallization behavior and morphological study of the polymeric membrane‐based repellent, were reported and discussed. Studies demonstrated that trapping of such repellents into microporous polymeric materials can be achieved by spinodal decomposition of the polymer/liquid repellent system. Usually, solubility is enhanced at elevated temperatures. Rapid cooling of such solution below the UCST leads to the formation of cocontinuous phase structures by decomposition. The polymer then forms an open‐cell structure with the repellent trapped inside. Approaches to forming such an open‐cell polymer structure containing mosquito repellent were successfully performed and confirmed with the SEM and POM techniques. It showed the structure of a polymer and liquid repellent prepared by spinodal decomposition, providing proof that thermally induced spinodal decomposition is a route to trap liquid mosquito repellent into a microporous polymer matrix. Additionally, the effects of polymer type, repellent nature, cooling conditions, and fillers on the morphology and performance of TIPS membranes are also discussed. Finally, challenges in developing microporous polymeric membrane‐based repellent using TIPS technology are addressed.

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Phase behavior of the polymer/drug system PLA/DEET: Effect of PLA molar mass on subambient liquid-liquid phase separation

Cited by 24 publications

References 38 publications

Crystallization of poly( l ‐lactic acid) in solution with the mosquito‐repellent N , N ‐diethyl‐3‐methylbenzamide

Crystallization of poly( l ‐lactic acid) in solution with the mosquito‐repellent N , N ‐diethyl‐3‐methylbenzamide

Bulk Enthalpy of Melting of Poly (l‐lactic acid) (PLLA) Determined by Fast Scanning Chip Calorimetry

A review on thermally induced phase separation technology in the fabrication of microporous polymer membrane devices for sustained‐repellent delivery: Crystallization and morphological studies

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