Films uniplanar orientation

Oriented films of polysaccharide crystallites have been prepared" " by first hydrolyzing the polysaccharide (cellulose, chitin) to obtain a colloidal dispersion of crystallites, and then either drying this to a film having uniplanar orientation or centrifuging it to form a permanently birefringent... 

Fig. 59. Ringfibre structure in a film. It is the case designated as selective uniplanar orientation by Sisson.

Venditto V, De Girolamo Del Mauro A, Mensitieri G, Milano G, Musto P, Rizzo P, Guerra G (2006) Anisotropic Guest Diffusion in the b Crystalline Host Phase of S5mdiotactic Polystyrene Transport Kinetics in Films with Three Different Uniplanar Orientations of the Host Phase. Chem. Mater. 18 2205-2210... 

Procedures suitable to prepare the different co-crystaUine phases with different morphologies are reviewed in this section. Particular attention will be devoted to film processing, because SPS co-crystals depending on their preparation procedure can assume three different kinds of iiniplanar orientation [69-75], The control of three different uniplanar orientations for a same polymer is possibly an unprecedented phenomenon. Part of this section (10.2.2.4) is devoted to SPS physical gels presenting co-crystalline phases as knots of their physical networks [76-87],... 

Films and Three Different Uniplanar Orientations of the Cocrystalline Phases Film processing in the presence of suitable solvents can lead to the formation of co-crystalline films exhibiting three different kinds of uniplanar orientations of the co-crystalline phases [69-75,95], The degree and the kind of uniplanar orientation depends on the selected technique (solution crystallization procedures or solvent-induced crystallization in amorphous... 

In fact, thorough analyses of X-ray diffraction patterns of SPS films exhibiting different crystalline and co-crystalline phases, and related evaluations of degrees of orientation, have allowed the conclusion that the three observed uniplanar orientations correspond to the three simplest orientations of the high planar-density ac layers (i.e., of close-packed alternated enantiomorphous SPS helices, Rg. 10.2a,b) with respect to the film plane. In particular, it has been proposed that the three uniplanar orientations of SPS should be named Ou cu, Uu Cj, and C//, indicating crystalline phase orientations presenting the a and c axes parallel (//) or perpendicular ( ) to the film plane (Hg. 10.2c-e) [75]. 

Information relative to quantitative evaluations of the uniplanar orientations [75] as well as to possible mechanisms leading to the three observed uniplanar orientations for SPS co-crystalline films, and their dependence on the crystallization technique and on the chemical nature of the guest, has been recently presented [71,75]. 

It is worth adding that suitable thermal treatments on SPS films presenting the three different uniplanar orientations of their helical crystalline phases can lead to films with planar orientations of their zigzag planar a [100-103] and (3 [104,105] crystalline phases [69,73], In particular, the transformation of the helices into trans-planar chains occurs maintaining their preferential orientation (parallel or perpendicular) with respect to the film surface [73],... 

The availability of SPS films with three different kinds of uniplanar orientation not only allows establishment of fine structural features of SPS crystalline and co-crystalline phases (e.g., experimental evaluation of the orientation of transition-moment-vectors of host and guest vibrational modes, with respect to the host chain axes) [106,107] but it can also be relevant for practical purposes. For instance, it allows guest orientation control [108,109] for cocrystalline phases and guest diffusivity (and hence permeability) control [97,98,110,111] for the nanoporous phases. (See following subsection 10.3.3.3). 

Due to the occurrence of a preferential orientation of guest molecules with respect to the host chain axes, the absorbance of the guest peaks is largely dependent on the different SPS orientations. As for 5 clathrates, for instance, the peaks corresponding to out-of-plane vibrational modes, whose transition-moment-vectors are nearly parallel to the chain axis, are of high intensity for the films where the c axis is in the film plane, that is, with an Cn and C// uniplanar orientations, and of low intensity for the films with an Ci orientation. 

As for possible applications of SPS co-crystalline films, particularly relevant is the possibility of achieving three different kinds of uniplanar orientation (see section 10.2.2.2), which allow control of the orientation of the guest molecules not only in the microscopic crystalline phase but also in macroscopic films. 

Figure 10.6 Schematic presentation of the orientation of the co-crystal chain axes (c) and of guest molecules, as obtained by p-nitro-aniline absorption in e form (a) and 6 form (b) films, presenting an ideal an Ci uniplanar orientation. (Reproduced with permission from Rizzo, E, Daniel, C., De Girolamo Del Mauro, A., Guerra, G. New host polymeric framework and related polar guest cocrystals. Chem. Mater., 19,3864—3866 (2007) [54]).

The reported sorption and desorption data not only conhrm that at low guest activities the sorption occurs nearly only by the nanoporous crystalline phase but also show that the guest transport behavior is dependent on the kind of uniplanar orientation of the host crystalline phase. In particular, in agreement with predictions based on molecular simulations [110], the lowest diffusivity has been measured for films with a Cu uniplanar orientation while the highest diffusivity has been measured for films with ai C// uniplanar orientation [97,98,111]. 

As for perspectives of applications of SPS-based co-crystaUine phases, studies will be mainly devoted to films, also trying to exploit the unique availability of three different kinds of uniplanar orientations, which allow macroscopic control of the guest orientation. Particular attention will be devoted to possible applications of the recently discovered e clathrates, mainly due the possibility of controlling the orientation of very long guest molecules, which could give relevant nonlinear optical properties. 

Venditto, V, De Girolamo Del Mauro, A., Mensitieri, G., Milano, G., Musto, R, Rizzo, R, Guerra, G. Anisotropic guest diffusion in the d crystalline host phase of syndiotactic polystyrene Transport kinetics in films with three different uniplanar orientations of the host phase. Chem. Mater., 18,2205-2210 (2006). 

It was therefore with some confidence in the infra-red and Raman spectroscopic methods that a much more complex investigation was carried out on the molecular orientation in one-way drawn PET films which show uniplanar axial orientation 5). In such films the condition of fibre symmetry is removed in two ways (1). There is no longer uniaxial symmetry of the distribution of chain axes. 

Very recently, SPS films with uniplanar-axial orientation of their cocrystalline phase with NP have been prepared and examined in detail [129] using Nishijima s method [142,143], where angular distribution of NP polarized fluorescence intensities was measured at each setting film angle by the... 

Itagaki, H., Sago, T., Uematsu, M., Yoshioka, G, Correa, A., Venditto, V, Guerra, G. Guest orientation in uniplanar-axial polymer host films and in cocrystal unit-cell, determined by angular distributions of polarized guest fluorescence. Macromolecules, 41, 9156-9164 (2008). 

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