Study of Polymer Blends with Sub-cluster Theory PartⅠ Essential Concepts and Equations of Sub-cluster Theory

Various viscosity-composition curves of polymer blends are summarized in eight groups. To represent these curves. 'sub-cluster equations' are derived on the basis of so called 'sub-cluster theoryThe essential concepts of sub-cluster theory and the derivation of those 'Sub-cluster equations' are briefly introduced.

COALESCENCE INDUCED GRADIENT MORPHOLOGY NEAR A WALL IN PHASE SEPARATED POLYMER BLENDS DURING QUIESCENT ANNEALING

A fast coalescence mechanism is proposed to account for the wall effect on the formation of gradient morphology in phase separated polymer blends during quiescent annealing. The existence of solid wall with high polarity is believed to change the potential field around the dispersed particles near the wall. This additional potential interaction between the solid wall and the dispersed particles causes faster coalescence of the dispersed particles near the wall than in the bulk. The gradient phase morphology thus formed can be predicted by combining the wall-particle interaction and the touch-coalescence mechanism. The effect of interfacial tension on the gradient morphology is also discussed.

Study of Polymer Blends with Sub-cluster Theory Part 2 Comparison of PVC/ABS, PVC/SBS Blends

Series of PVC/ABS and PVC/SBS blends of composition 20/ 80. 40/ 60, 60 / 40 and 80 / 20were prepared in a screw extruder. The phase morphology, miscibility and rheological behaviour of two systems were investigated. The viscosity-composition plots were represented by sub-cluster equation, the various differences between two systems are interpreted with the equation parameters

COMPATIBILITY IN POLYMER BLENDS OF POLY (VINYL ACETATE) AND POLY (METHYL METHACRYLATE)STUDIED BY NMR

Compatibility of poly (vinyl acetate) (PVAc) with poly (methyl methacrylate) (PMMA) mixtures has been studied by using nuclear magnetic relaxation, differential scanning calorimeter and small-angle X-ray scattering techniques. The nuclear magnetic relaxation time T_1's were measured as a function of composition in blends of PMMA and PVAc prepared from chloroform solution. The results show that the system is miscible for casting from chloroform solution.

EXPERIMENTAL INVESTIGATION OF THE LOW CYCLE FATIGUE CRACK PROPAGATION IN PC/ABS POLYMER BLENDS

Low cycle fatigue crack propagation (FCP) behavior of two PC/ABSblends with a weight ra- tio of PC to ABS being 80/20 and 60/40,respectively, is investigated. Experiments are carried out by usingstandard compact tension (CT) specimens. The fracture surfaces areexamined with a scanning electron mi- croscope (SEM). It is shownthat the FCP resistance of PC/ABS blend with 20/100 ABS particles ishigher than that of PC/ABS blend with 40/100 ABS particles. It isfound that proper ABS particle content can result in the tougheningof PC/ABS blends through particle cavitation and shear yielding inmatrix.

Studies on Droplet Size Distributions during Coalescence in Immiscible Polymer Blends Filled with Silica Nanoparticles

The effect of silica nanoparticles on the morphology of （10/90 wt%） PDMS/PBD blends during the shear induced coalescence of droplets of the minor phase at low shear rate was investigated systematically in situ by using an optical shear technique. Two blending procedures were used： silica nanoparticles were introduced to the blends by pre-blending silica particles first in PDMS dispersed phase （procedure 1） or in PBD matrix phase （procedure 2）. Bimodal or unimodal droplet size distributions were observed for the filled blends during coalescence, which depend not so much on the surface characteristics of silica but mainly on blending procedure. For pure （10/90 wt%） PDMS/PBD blend, the droplet size distribution exhibits bimodality during the early coalescence. When silica nanoparticles （hydrophobic and hydrophilic） were added to the blends with procedure l, bimodal droplet size distributions disappear and unimodal droplet size distributions can be maintained during coalescence; the shape of the different peaks is invariably Gaussian. Simultaneously, coalescence of the PDMS droplets was suppressed efficiently by the silica nanoparticles. It was proposed that with this blending procedure the nanoparticles should be mainly kinetically trapped at the interface or in the PDMS dispersed phase, which provides an efficient steric barrier against coalescence of the PDMS dispersed phase. However, bimodal droplet size distributions in the early stage of coalescence still occur when incorporating silica nanoparticles into the blends with procedure 2, and then coalescence of the PDMS droplets cannot be suppressed efficiently by the silica nanoparticles. It was proposed that with this blending protocol the nanoparticles should be mainly located in the PBD matrix phase, which leads to an inefficient steric barrier against coalescence of the PDMS dispersed phase; thus the morphology evolution in these filled blends is similar to that in pure blend and bimodal droplet size distributions can be observed during the early coalescence. These results imply that exploiting non-equilibrium processes by varying preparation protocol may provide an elegant route to regulate the temporal morphology of the filled blends during coalescence.

Crystalline Morphology and Crystallization Kinetics of Melt-miscible Crystalline/Crystalline Polymer Blends of Poly(vinylidene fluoride) and Poly(butylene succinate-co-24mol% hexamethylene succinate)

Poly（vinylidene fluoride） （PVDF） and poly（butylene succinate-co-24 mol% hexamethylene succinate） （PBHS）, both crystalline polymers, formed melt-miscible crystalline/crystalline polymer blends. Both the characteristic diffraction peaks and nonisothermal melt crystallization peak of each component were found in the blends, indicating that PVDF and PBHS crystallized separately. The crystalline morphology and crystallization kinetics of each component were studied under different crystallization conditions for the PVDF/PBHS blends. Both the spherulitic growth rates and overall isothermal melt crystallization rates of blended PVDF decreased with increasing the PBHS composition and were lower than those of neat PVDF, when the crystallization temperature was above the melting point of PBHS component. The crystallization mechanism of neat and blended PVDF remained unchanged, despite changes of blend composition and crystallization temperature. The crystallization kinetics and crystalline morphology of neat and blended PBHS were further studied, when the crystallization temperature was below the melting point of PBHS component. Relative to neat PBHS, the overall crystallization rates of the blended PBHS first increased and then decreased with increasing the PVDF content in the blends, indicating that the preexisting PVDF crystals may show different effects on the nucleation and crystal growth of PBHS component in the crystalline/crystalline polymer blends.

Measuring the Interfacial Thickness of Immiscible Polymer Blends by Nano-probing of Atomic Force Microscopy

Immiscible polymer blends are an important family of polymer materials.The interfacial thickness between different phases is a very important parameter that dictates,to a great extent,the morphology and properties of such a blend.This work explores and optimizes an up-to-date atomic force microscopy(AFM)of type NanoIR2^(TM) system in order to quantitatively measure the interfacial thickness of immiscible polymer blends.This system is equipped with two nano-probes capable of detecting the response of a material to an infrared pulse called AFM-infrared spectroscopy mode(AFM-IR)or conducting resonance called AFM-Lorentz Contact Resonance mode(AFM-LCR),respectively.Its potential for quantitatively measuring the interfacial thickness of immiscible polymer blends is evaluated using blends composed of polyamide 6(PA6)and polyolefin elastomer(POE)in the presence or absence of a POE containing maleic anhydride(POE-g-MAH)as a compatibilizer.Surface roughness affects adversely the signal intensity and consequently an accurate measurement of the interfacial thickness.Optimum sample surface preparation procedures are proposed.

Coalescence Suppression in Flowing Polymer Blends Using Silica Rods with Different Surface Chemistries

Silica rods with homogeneous(hydrophilic or hydrophobic)and amphiphilic surface properties were synthesized and their efficiencies in suppressing the flow-induced droplet coalescence of immiscible polyisobutylene(PIB)/polydimethylsiloxane(PDMS)blends were evaluated via in situ visualization technique.The flow-induced coalescence behavior of blends was found to strongly depend on the surface nature and concentration of silica rods added as well as the blend ratio.While a trace amount of rods promoted coalescence,all kinds of rods demonstrated a morphology refinement effect at high rod concentrations.Good compatibilization effects were obtained at high rod concentrations,especially for hydrophilic and amphiphilic rods.Based on confocal laser scanning microscopy results,these phenomena observed were interpreted reasonably in terms of the selective distribution and aggregation of silica rods,which were suggested to be decisive for the stabilization mechanism and efficiency of these rods.

Performance and Stability of Polymer Solar Cells Based on the Blends of Poly(3-Hexylthiophene) and Indene-C_(60) Bis-Adduct

The performance and morphology stability of polymer bulk heterojunetion solar cells based on poly（3-hexylthiophene） （P3HT） as the donor and indene-C6o bisadduct （ICBA） or methanofullerene [6,6]-phenyl C61-butyric acid methyl ester （PCBM） as the aeceptor are compared. Effect of the different donor and aeeeptor weight ratios on photo- voltaic performance of the P3HT：ICBA device is studied. The optimal device achieved power conversion emeiency of 5.51~o with dso of l0.86mA/cm2, Voc of 0.83 V, and fill factor （FF） of 61.1 % under AM 1.5G （lOOmW/cm2） simulated solar illumination. However, the stability measurement shows that cells based on P3HT：ICBA are less stable than those of the device based on P3HT：PCBM. Atomic force microscope results reveal that the morphol- ogy of the P3HT：ICBA film changed considerably during the storage periods due to unstable interpenetrating D-A network. This observation can be explained by the fact that there is lack of intermolecular hydrogen bonds in the P3HT：ICBA system. However, in the P3HT：PCBM system the molecules in the blend film are firmly held together in the solid state by means of intermoleeular hydrogen bonds originating from C-H. ~. Os bonds （where Os comes from the singly-bonded 0 atom of PCBM）, forming a stable three-dimensional network. The measured PL decay lifetimes for P3HT：PCBM and P3HT：ICBA systems are 33.66 ns and 35.34 ns, respectively, indicating that the P3HT：ICBA system has a less efficient exciton separation eftleiency than that of P3HT：PCBM, which may result in the interracial photogenerated charges accumulated on the D： A interface. Such progressive phase segregation between P3HT and ICBA eventually leads to the degradation in performance and deteriorates the stability of the device. We also present an approach to enhance the stability of P3HT：ICBA systems by adding PCBM as the second acceptor. Our results show that by carefully tuning the contents of PCBM as the second acceptor, more stable polymer solar cells can be obtained.

FRACTAL CHARACTER OF PHASE MORPHOLOGY OF HIGH IMPACT POLYSTYRENE/POLY(cis-BUTADIENE) RUBBER BLENDS

Evolution and fractal character of the phase morphology of high impact polystyrene/poly（cis-butadiene） rubber （HIPS/PcBR） blends during melting and mixing were investigated using scanning electron microscopy （SEM）. The characteristic length L was defined as the size of particles of the dispersed phase in blends. Different fractal dimensions, Df and Din, were introduced to study the distribution width of phase dimensions in the dimensionless region and the uniformity of the spatial distribution of particles, respectively. The results showed that the average characteristic length Lm and Df increase as the volume fraction of the dispersed phase increases, when the volume fraction of the dispersed phase is lower than 50%. In other words, the size of particles increases and their distribution in the dimensionless region becomes more uniform. Meanwhile, the uniformity of the spatial distribution becomes more perfect as the volume fraction increases. At a certain composition, Lm decreases in the initial stage of the mixing and levels off in the late stage. In the initial stage, Df becomes large rapidly with the process of blending, which means that the distribution of L in the dimensionless region becomes more uniform. Meanwhile, the spatial distribution tends to be ideal rapidly in the early stage and fluctuates in a definite range in the late stage of the mixing.

Thermal and Mechanical Properties of Thermoplastic Starch and Poly(Vinyl Alcohol-Co-Ethylene)Blends

The interest in thermoplastic starch(TPS)as a substitute material to replace conventional thermoplastics continues especially due its biodegradability,availability,low cost and because it is obtained from renewable sources.However,its poor mechanical properties and its high sensitivity to humidity have limited its use in several applications.Here,the copolymer poly(ethylene-co-vinyl alcohol)(EVOH),with two different ethylene contents,27 and 44 mol%were blended with TPS by extrusion in order to overcome these limitations.The obtained blends were characterized by thermogravimetric analysis(TGA),differential scanning calorimetry(DSC),mechanical tensile testing,Scanning Electron Microscopy(SEM)and moisture absorption test.The addition of EVOH copolymer did not significantly changed the thermal stability of TPS,however it increased the tensile strength in 65%when compared to TPS.The morphology of the blends did not showed two distinct phases,an indication of miscibility or partial miscibility of the components.A decrease of moisture absorption was obtained by the addition of EVOH and is more pronounced for the EVOH with 44% of ethylene.

COMPUTER SIMULATION OF MISCIBILITY AND SELF-ASSEMBLY STRUCTURE FOR POLYMER-CONTAINING SYSTEMS WITH SPECIAL INTERACTIONS

The miscibility and structure of A-B copolymer/C homopolymer blends with special interactions were studied by aMonte Carlo simulation in two dimensions. The interaction between segment A and segment C was repulsive, whereas it wasattractive between segment B and segment C. In order to study the effect of copolymer chain structure on the morphologyand structure of A-B copolymer/C homopolymer blends, the alternating, random and block A-B copolymers were introducedinto the blends, respectively. The simulation results indicated that the miscibility of A-B block copolymer/C homopolymerblends depended on the chain structure of the A-B copolymer. Compared with alternating or random copolymer, the blockcopolymer, especially the diblock copolymer, could lead to a poor miscibility of A-B copolymer/C homopolymer blends.Moreover, for diblock A-B copolymer/C homopolymer blends, obvious self-organized core-shell smicture was observed inthe segment B composition region from 20% to 60%. However if diblock copolymer composition in the blends is less than40%, obvious self-organized core-shell structure could be formed in the B-segment component region from 10 to 90%.Furthermore, computer statistical analysis for the simulation results showed that the core sizes tended to increasecontinuously and their distribution became wider with decreasing B-segment component.

Toughening of Immiscible rPS/SAN Blends by SEBS Elastomers: Properties and Morphology

In this research, an attempt was made to improve compatibility in a polymer blend composed of incompatible constituents, namely, recycled polystyrene (rPS) and polystyrene-co-acrylonitrile (SAN), through the addition of a compatibilizer. The compatibilizing agent, styrene-ethylenebutadiene-styrene block copolymer (SEBS), was added to the polymer blend in ratios of 5 and 10 wt%. For this purpose, blends of rPS and SAN at different ratios, without and with varying concentrations of compatibilizer, were prepared by melt blending using a co-rotating twin-screwextruder. Mechanical properties including tensile and impact strength, rheological properties (RPA), thermal behaviour (DSC) and morphological characteristics (SEM) were evaluated. According to the results obtained by complex viscosity, the blends behave as a pseudoplastic fluid. The results showed that the addition of SEBS increased the Izod impact strength and the elongation at break and decreased the tensile strength and tensile modulus. rPS/SAN blend modified with SEBS had better mechanical properties than the rPS/SAN alloy. SEM photographs revealed that the SEBS was not only distributed in the SAN phase but also distributed in rPS phase in rPS/SAN/SEBS blend. Furthermore, DSC analysis for blends of rPS/SAN gave a good indication of the improvement on miscibility for most compositions. SEM micrographs of tensile fracture surfaces indicated that the formation of the co-continuous phase and the improvement of interface adhesion are the most important reasons for the excellent tensile properties of the rPS/SAN/SEBS blends. Within the range of analysed compositions, the morphologies investigated by SEM are typical of immiscible blends.

Miscibility Behavior of Polyacrylamides Poly(Ethylene Glycol)Blends:Flory Huggins Interaction Parameter Determined by Thermal Analysis

Blends of polyacrylamide—PAM, poly(N-isopropylacrylamide)—PNIPAAm, poly(N-tert-butylacrylamide)—PTBAA, poly(N,N-dimethylacrylamide)—PDMAA and poly(N,N-diethylacrylamide)—PDEAA with poly(ethylene glycol)— PEG were prepared by casting in methanol and water at concentrations of 20 wt%, 40 wt%, 60 wt%, and 80 wt% in PEG. The miscibility of the components was studied by Differential Scanning Calorimetry—DSC. All blend systems are characterized by a single glass transition temperature (Tg), close to the Tg of the amorphous component. The Hoffman Weeks method was used to determine equilibrium melting temperature (Tm) data. The determination of the melt point depression of the blends allowed the calculation of Flory-Huggins interaction parameter (χ12) of the two polymers in the melt, by using the Nishi Wang equation. The interaction parameters, calculated for all the blends, are slightly negative and close to zero, suggesting a partial miscibility between the components.

A DYNAMIC MECHANICAL ANALYSIS STUDY OF THE TRANSITION BEHAVIOUR OF I-PP/EPDM BLENDS

The transition behaviour of the blends of isotactic polypropylene (i-PP) with ethylene-propylene terpolymer (EPDM) containing 42 wt% propylene was investigated by dynamic mechanical analysis technique (DMA). Owing to its high propylene content, EPDM is compatible with i-PP to some degree. The interaction between the two components was strengthened. As expected, for partially compatible system the glass transition temperature of i-PP in the blends shifted to lower temperature. It was found that there existed two transitions, αEPDM and βEPDM, for the EPDM used in this work. The former was considered to be the glass transition of the random chain segments of EPDM, while the latter the local motion of the long ethylene sequences in EPDM. The unusual transition behaviour of αEPDM in the blends was explained in terms of the greater thermal expansion of EPDM and the compatibility of the two components. On the other hand, the βEPDM changed with the composition of the blends in a regular manner.

Development of Biobased Poly(Lactic Acid)/Epoxidized Natural Rubber Blends Processed by Electrospinning: Morphological, Structural and Thermal Properties

This article reports the production of electrospun fibers from blends of poly(lactic acid) (PLA) and epoxidized natural rubber (ENR) solutions. The produced fibers were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA). SEM images showed the reduction in fiber size with ENR content of up to 25% in the mixture PLA/ENR. FTIR analysis revealed a possible interaction between carboxylic group of PLA and epoxi group of ENR. Thermal analysis showed the increase of the crystallinity fraction with ENR content and a decrease in thermal stability of eletrospun mats with the addition of ENR. The dynamic mechanical properties showed an enhancement of the stiffness of PLA/ENR blends with the increase of ENR content, which can support the production of interesting materials for tissue engineering based on renewable and biocompatible polymers. The reported properties indicate the possibility to use such fiber mats as potential materials in tissue engineering.

Study of Thermal,Phase Morphological and Mechanical Properties of Poly(L-lactide)-b-Poly(ethylene glycol)-b-Poly(L-lactide)/Poly(ethylene glycol)Blend Bioplastics

A poly(L-lactide)-b-poly(ethylene glycol)-b-poly(L-lactide)(PLLA-PEG-PLLA)block copolymer has great potential for use as a flexible bioplastic.Highly flexible bioplastics are required for flexible packaging applications.In this work,a PEG was incorporated into block copolymer as a plasticizer by solvent casting.PLLA-PEG-PLLA/PEG blends with different blend ratios were prepared,and the plasticizing effect and miscibility of PEG in block copolymer were intensively investigated compared to PLLA/PEG blends.The results indicated that the PEG was an effective plasticizer for the block copolymer.The blending of PEG decreased glass-transition temperature and accelerated the crystallization of both the PLLA and PLLA-PEG-PLLA matrices.The PEG was completely miscible when blended with block copolymer and it improved thermal stability of the block copolymer matrix but not of the PLLA matrix.Film extensibility of PLLA-PEG-PLLA/PEG blends steadily increased as the PEG ratio increased.These non-toxic and highly flexible PLLA-PEG-PLLA/PEG bioplastics are promising candidates for several applications such as biomedical devices,tissue scaffolds and packaging materials.

MONOMERIC INTERACTION BETWEEN ETHYLENE-TEREPHTHALATE AND CAPROLACTONE

The miscibility of poly(ethylene terephthalate (ET)- caprolactone (CL) (TCL)/poly(ethylene terephthalate) (PET) blends were examined by Differential Scanning Calorimeter (DSC). In these blends, a miscibility limit specified by ET content in the TCL was found to be about 70 (wt%). In the blends of TCL/TCL with different ET contents, a miscibility window defined by ET content was also found to range from 82 to 58 (wt%). Based on the experimental miscibility limits and the mean field binary interaction model, the interaction parameter between monomeric units of ET and CL was obtained.

Meniscus-Assisted Solution Printing Enables Cocrystallization in Poly(3-alkylthiophene)-based Blends for Field-Effect Transistors

The formation of cocrystallization in two various conjugated components may endow the newly formed conjugated cocrystals with multiple functionalities and improved charge transport properties.However,compared to conjugated small molecules,this strategy is rather limitedly realized in conjugated polymers.Herein,a simple meniscus-assisted solution printing(MASP)strategy is utilized to achieve the cocrystallization in the blends of two conjugated polymers,i.e.,poly(3-hexylthiophene)(P3HT)and poly(3-octylthiophene)(P3OT),and the cocrystalline structures are correlated closely to their charge mobilities.The P3HT/P3OT blends phase separate and crystallize individually in their drop-cast thin films.When subjecting the P3HT/P3OT blended solution to MASP,the confined solvent evaporation between two nearly parallel plates triggers them to cocrystallize progressively when accelerating the moving lower plate.The cocrystallization kinetics and the changes in P3HT/P3OT molecular structures are elucidated.Finally,these different crystalline structures of P3HT/P3OT blends are applied in organic fieldeffect transistors,imparting the cocrystallization-enhanced charge transport than respective P3HT and P3OT crystal domains.Such MASP method can be extended to craft cocrystals of other conjugated polymer blends for their diverse optoelectronic applications.