Spontaneous and Inductive Thickenings of Lamellar Crystal Monolayers of Low Molecular Weight PEO Fractions on Surface of Solid Substrates

Abstract

Crystalline macromolecules form folded-chain lamellar and metastable crystals. Annealing at a temperature below melting point results in a thickening of the metastable crystals to construct more stable ones. Such a process was visualized by AFM equipped with a hot stage in monolayers of poly(ethylene oxide) lamellar crystals on a silicon wafer surface. Our observations show that the monolayers can be thickened in a stepwise manner during stepwise heating to temperatures below the melting point. Our analyses show the thickening process and mechanism as follows: At the first step a small portion of the lamellar crystals have the capability to be spontaneously thickened into a thicker one at a certain temperature range, giving rise to a difference in lamellar thickness. In the following step the thinner lamellae are forced to melt, and then the melted molecules enter an amorphous phase in which they are transported toward the thicker lamellae and finally recrystallize in the thicker ones. This inductive mechanism is analogous to the evaporation−condensation mechanism.

Kinetic roughening transition and missing regime transition of melt crystallized polybutene-1 tetragonal phase: growth kinetics analysis

“…Prior to the crystallization at 85°C, the cast films used for the morphology observation in this work was heated up to 140°C, which is above the equilibrium melting temperatures of it-PB1 tetragonal and trigonal crystals. The crystals formed in the solution casting process became completely melted in the heating process before the crystallization at 85°C and the inductive thickening as reported by Zhai et al [29] does not participate in the crystal growth at 85°C. It was demonstrated by Fu et al with in-situ small angle X-ray scattering experiments of melt it-PB1 crystallization process that it-PB1 tetragonal crystals do not present spontaneous thickening during the isothermal crystallization.…”

“…At high supercooling conditions, the heat or mass diffusion field can play a key role in controlling the crystallization kinetics and crystal morphology. Zhai et al discovered temperature-independent crystallization patterns and morphologies in thin monolayer films of low molecular weight poly(ethylene oxide) (PEO) [29]. They demonstrated by in-situ atomic force microscopy observations that a competition exists between the monolayered lamellar crystals with different thicknesses in very thin films.…”

Thickening Processes of Lamellar Crystal Monolayers of a Low‐Molecular‐Weight PEO Fraction on a Solid Surface

“…It is argued that the sliding motion is the main mechanism of causing the ST and 1 st -IT thickening processes, while the 2 nd -IT process is associated with the meltingrecrystallization mechanism. [34] Relatively speaking, the sliding motion may be easier, so takes place during the low temperature range of the entire thickening process. The melting-recrystallization mechanism contains at least three courses: the melting of thin crystals, the diffusion of melted molecules to thick crystals, and the recrystallization into thick crystals.…”

“…[10,13,[17][18][19][20][22][23][24]26] The meltingrecrystallization mechanism emphasizes the melting of thin lamellae and the recrystallization of melted molecules to form thick lamellae. [8,11,20,21,26] In our previous study [34] we have demonstrated a quantized thickening process of a crystal monolayer of PEO with M n ¼ 5 000 g Á mol À1 on the surface of a silicon wafer when the samples were heated from room temperature to an annealing temperature. Our in-situ AFM observations have demonstrated that the thickening could be divided into spontaneous and inductive processes.…”

“…Figure 1 is a set of three-dimensional AFM images that highlight the main events found in our previous work. [34] The two images obtained at 30 and 34 8C show a fragmentation of a large dendritic crystal into many small crystals with different sizes. At the same time, the formation of two thicker and tapered areas, as pointed out by arrows A and B, shows a spontaneous thickening process from FC4 lamellae (with four folds) to EC lamellae that occurs in the temperature regime of 34 to 49 8C.…”