Modelling the impact of processing conditions on the kinetics of self assembly of soft multicomponent materials: effects of shear flow

我的目标是开发热力学和动量、热量和质量传输机制的概念和数学模型，这些机制决定了可食用多组分系统在不同外场(温度分布、剪切和拉伸流动等)下的自组装。剪切流在工业中的应用是非常有经验的，以获得所需的结构特性，但基本知识却很少。本应用主要用于由纯组份制备的多组份脂质体系的结晶。这将在一定程度上简化这些材料的多组分性质和多态的复杂性：即使是一个纯粹的组分也可以形成不同的固相。高温下的研究将着眼于粒子尺寸为纳米时的初始步骤，因为它们对粒子的空间分布至关重要，这将影响后期发生的所有结晶机制。在较低温度下的研究将包括多态转化。需要基于基本机理的模型，并且能够在流动和变温条件下工作。然而，文献中使用的少数模型没有这种灵活性。我最近开发了一个成功的棕榈油和牛奶脂肪在剪切作用下结晶的模型(例如，Phys。Rev.E.71,041607,2005年)，并建议检验该模型提出的假设：颗粒分离对生长/成核比的影响，过冷液体二次成核加速多晶型转变，以及分层结晶。为了检验这些假设，我们需要集成几种方法的测量，以提供原位和实时的定量相分布、颗粒特征和机械性能。我们将结合核磁共振、流变学和同步加速器X射线衍射。同时进行这些测量，将意味着多相体系结晶动力学研究的突破。这一发现对其他材料的聚集过程也非常有用，因为脂分子的大小介于大聚合物和小化合物之间。

I aim at developing conceptual and mathematical models for the thermodynamic and momentum, heat and mass transfer mechanisms that determine the self-assembly of edible multicomponent systems subject to different external fields (temperature profiles, shear and extensional flow, etc.). Shear flow is used very empirically in industry to obtain desired structural properties, but little fundamental knowledge exists. This application focuses on crystallization of multicomponent lipid systems prepared with pure components. This will somewhat simplify the complexity from the multicomponent nature and the polymorphism of these materials: even a pure component can form different solid phases. Studies at high temperature will look at the initial steps when the particles are nanometres in size, because they are crucial to the spatial distribution of particles, that will impact all the crystallization mechanisms occurring at later stages. Studies at lower temperatures will include polymorphic transformations. Models based on fundamental mechanisms and amenable to work under flow and variable temperature are required. Yet, the few models used in the literature do not have that flexibility. I recently developed a successful model for the crystallization of palm oil and milk fat under shear (e.g. Phys. Rev. E. 71, 041607, 2005), and propose to examine the hypotheses proposed with that model: impact of particle segregation on growth/nucleation ratios, acceleration of polymorphic transformations by secondary nucleation of undercooled liquid, and layered crystallization. To examine these hypotheses we require measurements that integrate several methods to provide quantitative phase distribution, particle characteristics and mechanical properties in-situ and in real time. We will combine NMR, rheology and synchrotron XRD. Done simultaneously these measurements will mean a breakthrough in the study crystallization kinetics of multi-phase systems. The findings will be very useful for aggregation processes in other materials as well since the lipid molecules have sizes between large polymers and small compounds.