Polychlorinated Next-generation Evolution Of The Crystalline Structure And Xylene Film High Temperatures

The Poly(chloro-p-xylylene), called PC films for short, have been polymer coating materials widely applied in semiconductor, Micro Electro Mechanical Systems,materials protection etc,because of their excellent barrier properties, anticorrosive property, low dielectric constant, Physical and mechanical properties. Crystalline structure, as the key factor affecting properties, is one of the major structure evolutions in PC films, the formation and the evolving law at elevated temperature of crystalline structure related to influencing properties have been the focus of study in Polymer science for the purpose of different applications.There have not been more analysis on the crystalline structure including crystal size,alignment and orientation of crystal and the evolution at elevated temperature, besides the cell structure and Surface topography. Studies on the relation between structure and performance are still inadequate.Under the same conditions, PC films as a function of film thickness of0.32μm、2.39μm、7.98μm、17.11μm、120μm were prepared by vapor deposition polymerization method, and precise correction of film thickness was made. The formation and stacking of crystalline structure in films was analyzed by synchrotron radiation facility (SRF), X-Ray diffractometer (XRD) and polarizing optical microscopy (POM). And then in the air and helium atmosphere some films as the thickness of17.5u m and120u m were annealed. The influence of different annealing temperature and time (0-480min) on the crystalline structure was investigated by X-Ray diffraction and infrared spectroscopy (IR) etc. The crystalline morphology, wettability, thermal and mechanical properties of PC films were analyzed by polarizing optical microscopy, atomic force microscope (AFM), differential scanning calorimetry (DSC), nano-indentation, contact angle meter. The results showed as follow.In PC thin films, the geometrical confinement and interfacial effect adsorbing molecular chain, result in slow diffusion velocity, the polymer crystal growth begin with a bundle, and favors more on the flat-on lamellar crystals. Crystallinity and crystal size increase as the film thickness rise, which makes crystalline phase more complete. Lamellar crystals change from the flat-on to the edge-on, and more molecular chain can be parallel to the substrate due to the weaker geometrical confinement and interfacial attractive interactions.After annealing in the air and helium atmosphere, the crystalline phase doesn’t change with the increase of temperature and time, the crystallinity and crystal size of PC films have been improved, simultaneously the concentration distribution of the edge-on lamellar crystals increases, the molecular chain is almostly parallel to the substrate plane.Not only dose the crystalline structure change, but also can the oxidation and thermal degradation exist,which give rise to the carbonyl and broken polymer molecular chains with the advance of annealing time in the air. Crystallization time lasts longer at250℃in the helium atmosphere, compared with in the air, whereas much more complete crystallinity is presented in PC films.The crystalline morphology, wetting, thermal and mechanical properties are influenced by the crystalline structure of films. Due to higher degree of crystallinity and orientation, the melting point, enthalpy of fusion, surface roughness, elastic modulus and indentation hardness rise up, but the contact angle decreases.During long period of annealing at250℃in the inert atmosphere, the quantity of crystal nucleus, grain size and enthalpy of fusion increase, and the elastic modulus and indentation hardness are unsteadily enhanced,but the melting point of films decline.Materials would be hardened and embrittled after annealed, with increasing rigidity of films; as for120u m PC films, the contact angle (<90°) is reduced and wettability is enhanced; the contact angle (>90°) rises slowly up and strong hydrophobicity is showed on17.5μm PC films, which closely related to the crystalline structure of films in the heat.