Defects in polydiacetylene single crystals

The structure of single crystals of a substituted polydiacetylene (pTS) has been investigated using transmission electron microscopy. The structure of the perfect crystal has been examined and it has been shown that the molecules lie in the plane of the lamellar crystals in an extended-chain conformation. The formations of bend contour zone axis patterns has been analysed and they are found to be due to the crystal being deformed into the shapes of both cups (or domes) and saddles. A common defect in the crystals was a stacking fault; using dark-field microscopy it has been found to have a displacement vector of 1/2 [1¯21]. It has been shown that such a stacking fault can be accommodated without any disruption to either the molecular backbone or the relatively large sidegroups on the molecule. The significance of these stacking faults with regard to the structure of polymer crystals in general is discussed.     

Electron microscopy of photo-oxidized polydiacetylene crystals

The photo-oxidation of toluene sulphonate polydiacetylene single crystals has been studied by scanning and transmission electron microscopy. Submicron particles were observed as reaction products on the surfaces of crystals which had been exposed to 514 nm light from an argon ion laser. Electron diffraction showed that these particles were single crystals ofparatoluene sulphonic acid. The appearance of the particles was correlated with the decrease in intensity of a Raman line associated with the presence of adsorbed oxygen on the crystal surface.     

Radiation damage and high resolution electron microscopy of polydiacetylene crystals

The relationship between radiation damage and the application of high resolution electron microscopy (HREM) to polydiacetylene single crystals has been examined. The damage is seen to occur by the decay of electron diffraction patterns and the loss of contrast in bright- and dark-field micrographs. The rate of damage was found to be different for the two polydiacetylene derivatives studied and to take place probably by cross-linking. It was found that lattice images from planes parallel to the chain direction with a spacing of 0.9±0.1 nm could be obtained from the most resistant derivative. Images of chain-end dislocations were obtained for the first time in a polymer crystal. The problems of applying HREM to polymers and the conditions for imaging individual molecules are discussed.     

Photo and pH dual-responsive polydiacetylene smart nanocontainer

Herein, a novel smart nanocontainer was developed by incorporating photo-responsive azobenzene derivative/cyclodextrin (Azo–CD) supramolecular complex into pH-responsive polydiacetylene (PDA) vesicles matrix. The designed nanocontainer exhibited excellent cell-toxicity, and the controlled release property response to external photo and pH stimuli. The photo-controlled inclusion and exclusion reaction between α-cyclodextrin (α-CD) and azobenzene moiety were used to act as the driving force to induce photo-triggered controlled release behavior of the designed nanocontainer. Moreover, the pH-responsive PDA vesicle matrix endowed the designed system with a controlled release property upon pH variation. The facile preparation procedures and their efficiency of response to the external stimuli render the novel smart nanocontainer potential candidate for future applications in remote controlled drug release.     

Optical properties of Langmuir-Blodgett polydiacetylene thin films

The colour phase transition of Langmuir-Blodgett polydiacetylene (LB PDA) films is investigated as a function of annealing temperature. A new reversible colour change is observed for a short annealing time. Such a reversible property has not previously been reported in LB PDA films. The X-ray diffraction patterns show that the reversible property is closely related to the layer structure of the LB films. Furthermore, the ratio of the line intensities of the Raman peaks due to C≡C and C=C stretch modes changes with the annealing temperature. The colour phase transition of the LB PDA films is correlated with this ratio. Such phase transitions have also been observed in laser-annealed points of LB PDA films. From these results, a new optical device based on LB PDA films is proposed. Furthermore, the electrical properties of ion-irradiated LB PDA films are briefly reported.     

Fluorescence signal enhancement of polydiacetylene vesicle stacks

Polydiacetylenes provide a good biological/chemical label-free detection system owing to their blue to red color change and fluorescence change from non-fluorescence to red fluorescence. One of the important factors to consider before applying polydiacetylenes to various sensors is to enhance the sensitivity against specific molecules. This paper reports two methods for stacking polydiacetylene vesicles for fluorescence signal enhancement of polydiacetylene on solid substrates. This focuses on how to achieve a highly sensitive sensor chip by introducing two strategies to immobilize the vesicles effectively on substrates. One method is layer-by-layer deposition through reactions of vesicles and avidins alternately on an avidin treated substrate. The other is to prepare a clustered vesicles solution by mixing the appropriate amount of a biotinylated vesicle solution and avidin solution, and then immobilize the clustered vesicles on the substrates. The former allows easy control of the layer thickness, whereas the latter can shorten the process time. These strategies can be applied to a range of biological/chemical sensors for fluorescence signal enhancement.     

Study of model polydiacetylene/epoxy composites

A model composite has been prepared consisting of a polydiacetylene single-crystal fibre in an epoxy resin matrix. The strain at points along the length of the fibre has been measured, using Raman spectroscopy, as a function of matrix strain and the post-cure temperature of the matrix. Good quantitative agreement has been found between the behaviour of the cold-cured system and the shear-lag model of Cox. The critical length of the fibres was measured as a function of fibre diameter and compared with recent calculations using finite difference methods. Higher post-cure temperatures have been shown to lead to compressive deformation of the fibres due to matrix shrinkage on cooling. The deformation is manifest as twinning, which disappears reversibly during tensile deformation. The amount of matrix shrinkage was determined by measuring the level of strain required to remove the twins. This was found to be in good agreement with the shrinkage determined from the linear thermal expansivity of the matrix.     

pH response of carboxy-terminated colorimetric polydiacetylene vesicles

Carboxy-terminated polydiacetylene vesicles are known to undergo dramatic color transitions in response to exposure to external stimuli such as pH, temperature, and receptor-ligand binding. FTIR spectroscopy was used to identify the breakdown in the interfacial hydrogen-bonding interactions of the carboxylic acid headgroups of polymerized 10,12-tricosadiynoic acid (TRCDA) vesicles in aqueous solution during pH chromic transition. The headgroup structure was monitored as the chromic transition takes place and the dissociation dependence of the pKa was determined. Due to the attenuated acidity of the interfacially confined carboxy groups, which exhibit pKa values in the range 9.5-9.9, it was found that the deprotonation-triggered blue-red chromic transition occurred in the pH range 9.0-10.1 and that the mechanism of the transition required interaction with the surface carboxyl group, which is of importance in the design of a biochromic mechanism using PDA assemblies. Transmission electron microscopy and FTIR spectroscopy revealed that the surface ionization and the pH-induced chromogenic transition was also accompanied by a dramatic vesicle-planar morphological transition alongside subtle changes to the alkyl chain conformation and packing. A two-step mechanism was implicated as causing the chromic transition that first involves surface deprotonation and then specific cation binding, which can aid the design of sensitive surface-ligand chemistry for new PDA structures.     

The study of model polydiacetylene/epoxy composites

A mode composite system consisting of one polydiacetylene single crystal fibre in an epoxy resin matrix has been subjected to tensile strain parallel to the fibre direction. The strain at all points along the length of the fibre was determined by resonance Raman spectroscopy while that of the matrix was measured by conventional techniques. Comparison of the fibre and matrix strain showed two distinct regions. Below about 0.5% matrix strain the composite followed Reuss-type behaviour with equal stress in the fibre and the matrix. At higher matrix strain the composite followed Voigt-type behaviour with any increase in matrix strain matched by an equal increase in fibre strain. In this region the strain distribution along the length of the fibre could be approximately described by the shear-lag model of Cox. The critical length of the fibre was found to increase linearly with fibre diameter as predicted by that model. Good qualitative agreement was found with the predictions of a calculation based on finite element analysis over the full range of applied stress.     

Micro-contact printing of polydiacetylene liposomes using hydrophilic stamps

Micron-sized polydiacetylene (PDA) liposome patterns have been fabricated on titanium (Ti) substrates using a micro-contact printing (micro-CP) technique. Two types of stamps (PDMS and agarose) and inking methods ("soaking" and "dropping") are used for micro-CP, and we compare their effect on the morphology of the PDA patterns. The size and morphology of the patterned PDA liposomes are analysized by optical and fluorescence microscopies and atomic force microscopy (AFM). When the agarose stamp is inked by the "dropping" method, PDA patterns are most efficiently transferred to the Ti substrate. However, the thickness of the transferred PDA patterns is not homogeneous, with the edge of the transferred pattern being thicker than its center. In contrast, when the PDMS stamp is used for micro-CP, the center of the pattern is thicker than the edge. Red fluorescence patterns are readily obtained by heat treatment of the PDA-immobilized solid substrate. The intensity of the fluorescence of the samples is consistent with the results of optical microscopy and AFM experiments.     

The study of model polydiacetylene/epoxy composites

Raman spectroscopy and conventional mechanical testing have been employed to study a range of polydiacetylene fibre composite specimens with varying volume fractions cured at either room temperature for a week or at 100 C for 24 h. The high-temperature cured composites were found to contain thermal stresses sufficient to cause twinning in the polydiacetylene fibres which affected the mechanical response of the bulk composite. A simple modification to discontinuous fibre reinforcement theory which accounts for the effect of thermal stresses in the material has been presented, giving good agreement with the experimental data. Small cracks were found to be produced at the end of the fibres by thermal stresses.     

Structural change of polydiacetylene Langmuir film during compression process

The conformational change and the alignment behavior of poly-4BCMU were investigated in compression, de-compression and re-compression process using LB method. In compression process, the conformation of poly-4BCMU changed from random-coil conformation to rigid-rod one. With the increase of surface pressure, poly-4BCMU with rigid-rod conformation gathered into bundles and they aligned perpendicular to the compressing direction. Once stopping the compression and releasing the surface pressure, the bundle textures released packing. In this process (de-compression process), the conformational change never occurred. Discrete slender fibrils gathered again in re-compression process, resulting in the formation of close-packed bundles with high molecular ordering.     

Bleaching of exciton transition in Langmuir-Blodgett films of polydiacetylene

Saturation absorption measurements with laser pulses of a few picosecond duration performed on thin Langmuir-Blodgett films of polydiacetylene blue form at the absorption band are reported and discussed. The measurements give directly the imaginary part of the Kerr susceptibility χ⁽³⁾(-ω;ω,ω,-ω) which is found to be very large (in excess of 10^-8 e.s.u.) with a fast response time. The results are discussed in terms of the phase-space-filling exciton model.     

Hyperfine structure of magnetic-resonance electrical conductivity of doped polydiacetylene

Magnetic resonance with a hyperfine structure which can be detected from the electrical conductivity has been observed in iodine-doped polydiacetylene films. This resonance is attributable to transitions between Zeeman levels in the spin-dependent carrier transfer process in a system of localized paramagnetic centers. Pis’ma Zh. Tekh. Fiz. 25, 86–90 (December 12, 1999)     

Lipid/polydiacetylene films for colorimetric protein surface-charge analysis

The distribution and organization of charges on a protein surface are fundamental properties which affect protein functions and interactions. We demonstrate a new approach for protein surface-charge analysis through modulating protein interactions with chromatic lipid/polydiacetylene (PDA) films. We show that visible and easily quantifiable blue-red transitions, induced on the film surface through electrostatic interactions between the negatively charged PDA and positive soluble species, constitute an effective means for characterizing protein surface charge. Specifically, protein-film interactions can be significantly modulated by complexation between the tested macromolecules and lipid-embedded multivalent calixarene ligands displaying charged residues, making possible protein discrimination based upon the abundance and organization of surface charge. The lipid/PDA film system, in conjunction with the calixarene-derived ligands, facilitates characterization of protein surface charges and identification of anomalous protein electrostatic properties.     

Stress induced twinning of polydiacetylene single crystal fibres in composites

Scanning electron microscopy has been used to show that twins induced by compression of DCHD-polydiacetylene fibres occur on a single crystallographic plane. Other twinning modes appear to be prohibited by the nature of the sidegroup packing. Under the optical microscope identical twinning patterns have been observed on fibres in composite specimens where matrix shrinkage had been induced by post-curing the epoxy at 100°C. Resonance Raman spectroscopy has been used to monitor the strain in a single fibre embedded in an epoxy matrix which was subjected to uniaxial compressive stress. The initiation of twinning was found to occur when the axial strain in the fibre was approximately 0.2%.     

Tumor-targeted polydiacetylene micelles for in vivo imaging and drug delivery

In vivo tumor targeting and drug delivery properties of small polymerized polydiacetylene (PDA) micelles (～10 nm) is investigated in a murine MDA-MB-231 xenograft model of breast cancer. Three micelles with different surface coatings are synthesized and tested for their ability to passively target tumor through the enhanced permeability and retention effect. After injection (24 h), fluorescence diffuse optical tomographic imaging indicates a tumor uptake of nearly 3% of the injected dose for the micelles with a 2 kDa poly(ethylene glycol) (PEG)-coating (PDA-PEG2000). The uptake of PDA micelles in tumors is confirmed by co-localization with [(18) F]-fluorodeoxyglucose (FDG) positron emission tomography. Although FDG has a higher diffusion rate in tumors, 40 ± 19% of the retained micelles is co-registered with the tumor volume visualized by FDG. Finally, PDA-PEG2000 micelles are loaded with the hydrophobic anticancer drug paclitaxel and used in vivo to inhibit tumor growth. These findings demonstrate the potential of PDA-PEG2000 micelles for both in vivo tumor imaging and drug delivery applications.     

Synthesis and characterization of monodispersed polymer/polydiacetylene nanocrystal composite particles

Monodispersed polymer/polydiacetylenecomposite particles were synthesized by soap-free seeded emulsion polymerization of styrene andmethyl methacrylate; the products were characterized by XRD, SEM, TEM, UV-visible spectroscopy, and single particle scattering spectroscopy. In the synthesis process, polydiacetylene nanocrystals were found to act as inhibitor, and consequently a relatively low concentration was necessary. Different monomers lead to the differences in reaction condition and particle morphology; the PMMA composite particles were simpler in preparation than polystyrene particles, but the latter havebetter spherical morphology. The composite particles were composed of polymer shells and polydiacetylene cores, which kept their crystal structure and optical properties. A high percentage of cored particles could be achieved with optimized reaction conditions where the amount of seed was sufficient and the oily oligomer by-product was suppressed.