**1. Introduction**

640 Thermodynamics – Interaction Studies – Solids, Liquids and Gases

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A scientific understanding of the behaviour of polymers under extreme conditions of temperature and pressure becomes inevitably of the utmost importance when the objective is to produce materials with well-defined final in-use properties and to prevent the damage of materials during on-duty conditions. The proper properties as well as the observed damages are related to the phase transitions together with intimate pattern organization of the materials.

Thermodynamic and thermokinetic issues directly result from the thermodynamic independent variables as temperature, pressure and volume that can stay constant or be scanned as a function of time. Concomitantly, these variables can be coupled with a mechanical stress, the diffusion of a solvent, and/or a chemically reactive environment. A mechanical stress can be illustrated in a chemically inert environment by an elongation and/or a shear. Diffusion is typically described by the sorption of a solvent. A chemical environment is illustrated by the presence of a reactive environment as carbon dioxide or hydrogen for example.

Challenging aspects are polymer pattern multi scale organizations, from the nanometric to the macrometric scale, and their importance regarding industrial and technological problems, as described in the state of the art in Part 2. New horizons and opportunities are at hands through pertinent approaches, including advanced *ad hoc* experimental techniques with improved modelling and simulation. Four striking illustrations, from the interactions between a solvent and a polymer to the growth patterns, are illustrated in Part 3.

Thermodynamics and Thermokinetics to Model Phase Transitions of Polymers

**Cross fertilization between polymer crystallization and metal solidification** 

Physical chemists and metallurgists alike are constantly confronted with materials properties related to (polymer) crystallization (*e.g.*, spherulite size distribution, lamellae spacing) or (metal) solidification (*e.g.*, grain size distribution, dendrite arm or eutectic spacing), respectively. In metal science, if accurate numerical modelling of dendritic growth remains a major challenge even with today's powerful computers, the growth kinetic theories, using accurate surface tension and/or kinetic anisotropies, are well advanced (Asta et al., 2009; Flemings, 1974). In polymer science, such approaches exist. But still insight into the physics/kinetics connection and morphologies is little known (Piorkowska et al., 2006). The most well-known growth kinetics theory is the one of Hoffman and coworkers (Hoffman, 1983) which is based on the concept of secondary nucleation; the nucleation and overall kinetics of crystallization have been also intensively studied (Avrami, 1939, 1940,

The multi-length scale and semi-crystalline structure organizations are intimately linked with the chemical, physical, mechanical integrity and failure characteristics of the materials.

Semi-crystalline polymers gain increasing importance in manufacturing (extended to recycling) industries where the control at the nano- to micro- up to macrometric hierarchical levels of the patterns constitutes a major engineering challenge (Lo et al., 2007). The domains extend from optics, electronics, magnetic storage, isolation to biosorption, medicine, packaging, membranes and even food industry (Rousset et al., 1998; Winter et al., 2002; Park et al., 2003; Nowacki et al., 2004; Scheichl et al., 2005; Sánchez et al., 2007; Wang et al.,

Industrial polymer activities, through processes like, for instance, extrusion coating (*i.e.*, the food industry with consumption products), injection moulding (*i.e.*, the industry with

lamellae/amorphous layer.

2010).

1941; Binsbergen, 1973; Haudin & Chenot, 2004).

**Polymers with well-defined end-used properties** 

**Control of polymer structure in processing conditions** 

**2.1.2 Practical applications, importance of crystal organization** 

over Extended Temperature and Pressure Ranges Under Various Hydrostatic Fluids 643

In polymer physics, the spherulitic crystallization **(Fig. 1.c)** represents a classic example of pattern formation. It is one of the most illustrated in the literature. Besides their importance in technical polymers, spherulitic patterns are also interesting from a biological point of view like semicrystalline amyloid spherulites associated with the Alzheimer and Kreutzfeld-Jacob diseases (Jin et al., 2003; Krebs et al., 2005). The spherulitic pattern depends on polymer chemistry (Ferreiro et al., 2002b). Stereo irregular atactic or low molecular weight compounds are considered as impurities, which are rejected by growing crystals. The openness of structure, from spherulite-like to dendrite-like, together with the coarseness of texture (a measure of the 'diameters' of crystalline fibres between which impurities become concentrated during crystal growth) was illustrated in the work of Keith & Padden (1964). These processes induce thermal and solute transport. Thus pattern formation is defined by the dynamics of the crystal/melt interface involving the interfacial energy. In the nanometric scale domain, spherulite is a cluster of locally periodic arrays of crystalline layers distributed as radial stacks of parallel crystalline lamellae separated by amorphous layers **(Fig. 1.b)**. Molecular chains through the inter-lamellar amorphous layers act as tie molecules between crystalline layers, making a confined interphase crystalline
