Enthalpy of fusion of poly(3‐hexylthiophene) by differential scanning calorimetry

The enthalpy of fusion for a perfect, infinite poly(3‐hexylthiophene) (P3HT) crystal () must be known to evaluate the absolute crystallinity of P3HT. This value, however, is still ambiguous as different values have been reported using various experimental techniques. Here, we extrapolate the enthalpy of fusion for extended chain crystals of oligomeric P3HT to infinite molecular weight and obtain a value of 42.9 ± 2 J/g employing differential scanning calorimetry with a correction based on grazing incidence small angle X‐ray scattering data. Also, we define the onset of chain folding within P3HT crystallites at a chain length of 5 Kuhn segments. Knowledge of allows calculation of P3HT percent crystallinity in thin films for applications such as organic field effect transistors and solar cells. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1469–1475     

Structure and morphology control in thin films of regioregular poly(3‐hexylthiophene)

This review focuses on the structural control in thin films of regioregular poly(3‐hexylthiophene) (P3HT), a workhorse among conjugated semiconducting polymers. It highlights the correlation existing between processing conditions and the resulting structures formed in thin films and in solution. Particular emphasis is put on the control of nucleation, crystallinity and orientation. P3HT can generate a large palette of morphologies in thin films including crystalline nanofibrils, spherulites, interconnected semicrystalline morphologies and nanostructured fibers, depending on the elaboration method and on the macromolecular parameters of the polymer. Effective means developed in the recent literature to control orientation of crystalline domains in thin films, especially by using epitaxial crystallization and controlled nucleation conditions are emphasized. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1218–1233, 2011     

Glass transition temperature of thin polycarbonate films measured by flash differential scanning calorimetry

Flash differential scanning calorimetry was used to study the glass transition temperature T_g of polycarbonate ultrathin films. The investigation was made as a function of film thickness from 22 to 350 nm and over a range of cooling rates from 0.1 to 1000 K/s. Polycarbonate spin cast films were floated on a layer of grease on the calorimetric chip. The results show a greatly reduced glass temperature for the thinnest films relative to the macroscopic value. We also observed that the magnitude of the glass temperature reduction decreases as the cooling rate increases with the highest cooling rates showing little thickness dependence of the T_g. Dynamic fragility and activation energy at T_g were found to decrease with decreasing film thickness. The results are discussed in the context of literature reports for supported and freely standing polycarbonate films. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1462–1468     

Nucleation and crystallization kinetics of polyamide 12 investigated by fast scanning calorimetry

Nucleation and crystallization of polyamide 12 (PA 12) have been systematically investigated by fast scanning calorimetry at non-isothermal and isothermal conditions. The critical cooling rates of crystallization and crystal nucleation were determined as 300 and 10,000 K/s, respectively. Moreover, the half-times of nucleation (t_1/2,nucl) and overall crystallization (t_1/2,cry) show monomodal and bimodal dependencies on the crystallization temperature. t_1/2,nucl has an approximate minimum value of about 0.0005 s at 333 K, which is about 10–20 K above the glass transition temperature, and t_1/2,cry has two minima of about 0.05 and 0.8 s at about 333 and 383 K, respectively. Comparing the crystallization behavior of PA 12 with other polyamides, the activation energy for crystallization increases and the energy barrier of short-range diffusion decreases with the increase of the amide-group density in the chains.     

Secondary doping in poly(3,4‐ethylenedioxythiophene):Poly(4‐styrenesulfonate) thin films

The electrical and structural properties of poly(3,4‐ethylenedioxythiophene):poly(4‐styrenesulfonate) (PEDOT:PSS) thin films deposited from aqueous dispersion using different concentrations of selected secondary dopants are studied in detail. An improvement of the electrical conductivity by three orders of magnitude is achieved for dimethyl sulfoxide, sorbitol, ethylene glycol, and N,N‐dimethylformamide, and the secondary dopant concentration dependence of the conductivity exhibits almost identical behavior for all investigated secondary dopants. Detailed analysis of the surface morphology and Raman spectra reveals no presence of the secondary dopant in fabricated films, and thus the dopants are truly causing the secondary doping effect. Although the ratio of benzenoid and quinoid vibrations in Raman spectra is unaffected by doping, the phase transition in PEDOT:PSS films owing to doping is confirmed. Further analysis of temperature‐dependent conductivity reveals 1D variable range hopping (VRH) charge transport for undoped PEDOT:PSS, whereas highly conductive doped PEDOT:PSS films exhibit 3D VRH charge transport. We demonstrate that the charge ‐ hopping dimensionality change should be a fundamental reason for the conductivity enhancement. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1139–1146     

Effects of evaporation velocity and film thickness on poly(3‐hexylthiophene) thin films processed from aggregate dispersions in binary solvent mixtures

Aggregate dispersions of P3HT in two series of solvent mixtures, chloroform:dichloromethane and toluene:dichloromethane, are used to study the impact of the evaporation velocity and film thickness on the P3HT films processed using two spin‐coating speeds (1000 rpm and 2000 rpm). The structural order and surface morphology were investigated with UV/Vis absorption spectroscopy and atomic force microscopy techniques. There is no evidence that the characteristics of the liquid phase P3HT dispersions impact the structures of the films, which is in agreement with a previous study of drop cast P3HT films that were dried over much longer time periods. An association is observed between the extent of aggregation in the liquid phase and the thickness and surface roughness parameters of the films. However, the structural order does not correlate with the thickness of the films, which was previously reported for polymer films processed from amorphous polymer solutions in pure organic solvents. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 330–343     

Probing the early stages of thermal fractionation by successive self‐nucleation and annealing performed with fast scanning chip‐calorimetry

The thermal fractionation kinetics of a linear low‐density polyethylene (LLDPE) during Successive Self‐Nucleation and Annealing (SSA) is investigated by fast scanning chip‐calorimetry (FSC), by systematically varying the holding times (t_s) at each fractionation temperature (T_s). The range of explored fractionation times spans four orders of magnitude, from 0.001 to 10 s. Discernible thermal fractions are already detected in the very early stages of the process, at t_s shorter than one second. As t_s increases, the melting endotherm after SSA indicates a progressive lamellar thickening and narrowing of the thicknesses distribution of the various crystalline fractions. The largest variations are observed for the families of crystals containing the longest crystallizable sequences, which also undergo a change of their relative content as a consequence of self‐nucleated crystallization at T_s. The quality of the thermal fractionation obtained in 10 seconds with FSC is equivalent to that of conventional differential scanning calorimetry SSA (t_s = 300 s). © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 2200–2209     

The effect of self-nucleation on isothermal crystallization kinetics of poly(butylene succinate) (PBS) investigated by differential fast scanning calorimetry

Differential fast scanning calorimetry (DFSC) was employed on the study of self-nucleation behavior of poly(butylene succinate) (PBS).The ultra-fast cooling ability of DFSC allows investigating the effect of self-nucleation on the isothermal crystallization kinetics over a wide temperature range.Crystallization half-time,instead of crystallization peak temperature,was used to describe the self-nucleation behavior,and the self-nucleation domain for the samples crystallized at different temperatures was determined.Due to the competition between homogenous nucleation and self-nuclei,the effect of self-nucleation was less pronounced at high supercooling than that for the sample isothermally crystallized at higher temperature.An efficiency scale to judge the efficiency of nucleating agents from the crystallization half-time was also introduced in this work.     

Temperature‐modulated differential scanning calorimetry studies on the origin of double melting peaks in isothermally melt‐crystallized poly(L‐lactic acid)

In this work, the melting behaviors of nonisothermally and isothermally melt‐crystallized poly(L ‐lactic acid) (PLLA) from the melt were investigated with differential scanning calorimetry (DSC) and temperature‐modulated differential scanning calorimetry (TMDSC). The isothermal melt crystallizations of PLLA at a temperature in the range of 100–110 °C for 120 min or at 110 °C for a time in the range of 10–180 min appeared to exhibit double melting peaks in the DSC heating curves of 10 °C/min. TMDSC analysis revealed that the melting–recrystallization mechanism dominated the formation of the double melting peaks in PLLA samples following melt crystallizations at 110 °C for a shorter time (≤30 min) or at a lower temperature (100, 103, or 105 °C) for 120 min, whereas the double lamellar thickness model dominated the formation of the double melting peaks in those PLLA samples crystallized at a higher temperature (108 or 110 °C) for 120 min or at 110 °C for a longer time (≥45 min). © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 466–474, 2007     

Thermal memory of poly(3‐hydroxybutyrate) using temperature‐modulated differential scanning calorimetry

The influence of thermal history on morphology, melting, and crystallization behavior of bacterial poly(3‐hydroxybutyrate) (PHB) has been investigated using temperature‐modulated DSC (TMDSC), wide‐angle X‐ray diffraction (WAXRD) and polarized optical microscopy (POM). Various thermal histories were imparted by crystallization with continuous and different modulated cooling programs that involved isoscan and cool–heat segments. The subsequent melting behavior revealed that PHB experienced secondary crystallization during heating and the extent of secondary crystallization varied with the cooling treatment. PHB crystallized under slow, continuous, and moderate cooling rates were found to exhibit double melting behavior due to melting of TMDSC scan‐induced secondary crystals. PHB underwent considerable secondary crystallization/annealing that took place under modulated cooling conditions. The overall melting behavior was interpreted in terms of recrystallization and/or annealing of crystals. Interestingly, the PHB analyzed by temperature modulation programs showed a broad exotherm before the melting peak in the nonreversing heat capacity curve and a multiple melting reversing curve, verifying that the melting–recrystallization and remelting process was operative. WAXRD and POM studies supported the correlations from DSC and TMDSC results. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 70–78, 2006     

Growth of poly(3,4‐ethylenedioxythiophene) films prepared by base‐inhibited vapor phase polymerization

Transparent [90% transmittance at 550 nm at a sheet resistance (R_s) of 279 Ω sq^?1] poly(3,4‐ethylenedioxythiophene) (PEDOT) films with electrical conductivities up to 1354 S cm^?1 are prepared using base‐inhibited vapor phase polymerization at atmospheric pressure. The influence of reaction conditions, such as temperature and growth time, on the film formation is investigated. A simple and convenient two‐electrode method is used for the in situ measurement of resistance, enabling to investigate the growth mechanism of polymer films and the influence of different parameters (relative humidity and the amount of oxidant) on the film growth. Low humidity exerts a detrimental effect on film growth and conductivity. In situ R_s measurements suggest that a large structural change occurs upon washing the PEDOT‐oxidant film. © 2014 Wiley Periodicals, Inc. J Polym Sci Part B: Polym. Phys. 2014 , 52, 561–571     

Free‐volume and crystallinity in low molecular weight poly(ethylene oxide)

Positron annihilation lifetime spectroscopy (PALS), differential scanning calorimetry, X‐ray diffraction, and polarized light optical microscopy were used to study six low molar mass poly(ethylene oxide) samples with average molar masses ranging from 1 × 10³ to 10 × 10³ g mol^?1. Dynamic light scattering was used to determine molar mass and polydispersity rigorously. Polymer samples with 70–95% crystallinity, which is an unusual range in PALS studies, were prepared by molten material quenching. The ortho‐positronium pick‐off lifetime (τ₃) and relative fractional free volume (f_v), determined by the free volume model, correlated well with the average molar mass and crystallinity of the polymers. X‐ray diffraction and polarized light optical data support the interpretation of positron annihilation results. PALS parameter, I₃, which is associated with high cavity content, remained approximately constant at 20–22% for all samples. The cavities are present as crystallite defects in the spherulitic open texture and the amorphous phase for the low crystallinity sample (e.g., for M_w = 1390) and at the interfaces and in interlamellar spherulite regions of the more crystalline materials. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2400–2409, 2007     

Nonisothermal crystallization and melting behavior of a luminescent conjugated polymer,poly(9,9‐dihexylfluorene‐alt‐co‐2,5‐didecyloxy‐1,4‐phenylene)

The nonisothermal crystallization kinetics of a luminescent conjugated polymer, poly(9,9‐dihexylfluorene‐alt‐co‐2,5‐didecyloxy‐1,4‐phenylene) (PF6OC10) with three different molecular weights was investigated by differential scanning calorimetry under different cooling rates from the melt. With increasing molecular weight of PF6OC10, the temperature range of crystallization peak steadily became narrower and shifted to higher temperature region and the crystallization rate increased. It was found that the Ozawa method failed to describe the nonisothermal crystallization behavior of PF6OC10. Although the Avrami method did not effectively describe the nonisothermal crystallization kinetics of PF6OC10 for overall process, it was valid for describing the early stage of crystallization with an Avrami exponent n of about 3. The combined method proposed in our previous report was able to satisfactorily describe the nonisothermal crystallization behavior of PF6OC10. The crystallization activation energies determined by Kissinger, Takhor, and Augis‐Bennett models were comparable. The melting temperature of PF6OC10 increased with increasing molecular weight. For low‐molecular‐weight sample, PF6OC10 showed the characteristic of double melting phenomenon. The interval between the two melting peaks decreased with increasing molecular weight, and only one melting peak was observed for the high‐molecular‐weight sample. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 976–987, 2007     

Crystallinity and crystalline phase orientation of poly(1,4‐cis‐isoprene) from Hevea brasiliensis and Taraxacum kok‐saghyz

Crystallization is studied for poly(isoprene‐1,4‐cis) from Hevea brasiliensis (natural rubber [NR]) and from taraxacum kok‐saghyz, mainly by collecting wide‐angle X‐ray diffraction patterns after processing and stretching. Although rubber samples before stretching are generally fully amorphous, crystallization can be induced in NR samples by processing at room temperature under moderate pressure. This phenomenon is possibly associated with nucleation by saturated fatty acid components. For rubber samples being fully amorphous in the undeformed state, strain‐induced crystallization occurs only at high strain ratios (α > 4), leading to high degrees of crystalline phase orientation (f_c > 0.9 for α = 5). Rubber samples presenting some crystallinity already in the unstretched state, on the contrary, reach much lower degrees of axial orientation, even for high strain ratios (f_c < 0.7 for α = 5). These differences in crystallinity and in crystalline phase orientations produce large differences in stress–strain behavior of the rubber. By room temperature processing, the considered NR samples can also develop an unreported disordered crystalline modification, with low intensity of 120 and 121 reflections. This disordered crystalline modification, which is also maintained after axial stretching procedures, can rationalized by a structural disorder along the b axis, possibly associated with statistical sequences of A⁺TA^? or A^?T A⁺ conformations for poly(isoprene‐1,4‐cis) chains. Copyright © 2016 John Wiley & Sons, Ltd.     

Crystallization and melting of poly(oxyethylene) analyzed by temperature-modulated calorimetry

Temperature-modulated calorimetry, TMC, is used to evaluate the temperature region of metastability between crystallization and melting. While crystals like indium can be made to melt practically reversibly during a TMC cycle of low amplitude so that sufficient crystal nuclei remain unmelted, linear macromolecules cannot, because of their need to undergo molecular nucleation. Modulation amplitudes varying from ±0.2 to ±3.0 K are used to assess the temperature gap between the slow crystallization region and the melting of metastable crystals of poly(oxyethylene) (PEO) of molar mass 1500 Da. This low molar mass PEO serves as a model compound with a metastable gap of melting/crystallization that can be bridged by TMC with a large modulation amplitude. © 1997 John Wiley & Sons, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

J Polym Sci B: Polym Phys 35 : 1877–1886, 1997     

Nonisothermal crystallization kinetics of biodegradable poly(butylene succinate‐co‐propylene succinate)s

Poly(butylene succinate) (PBSu) and two poly(butylene succinate‐co‐propylene succinate)s were synthesized via the direct polycondensation reaction. The copolyesters were characterized as having 7.0.and 11.5 mol % propylene succinate (PS) units, respectively, by ¹H NMR. A differential scanning calorimeter (DSC) and a polarized light microscope (PLM) adopted to study the nonisothermal crystallization of these polyesters at a cooling rate of 1, 2, 3, 5, 6, and 10 °C/min. Morphology and the isothermal growth rates of spherulites under PLM experiments were monitored and obtained by curve‐fitting. These continuous rate data were analyzed with the Lauritzen?Hoffman equation. A transition of regime II → III was found at 95.6, 84.4, and 77.3 °C for PBSu, PBPSu 95/5, and PBPSu 90/10, respectively. DSC exothermic curves show that all of the nonisothermal crystallization occurred in regime III. DSC data were analyzed using modified Avrami, Ozawa, Mo, Friedman, and Vyazovkin equations. All the results of PLM and DSC measurements indicate that incorporation of minor PS units into PBSu markedly inhibits the crystallization of the resulting polymer. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1299–1308, 2010     

Poly(3‐hexylthiophene) aggregation at solvent–solvent interfaces

The aggregation behavior of P3HT is investigated at the interface of orthogonal solvents for P3HT. The changeable characteristics of P3HT aggregate dispersions, for example, extent of aggregation and intrachain order, are studied by varying (1) the interfacial area, (2) the poor solvent used to induce aggregation – dichloromethane (DCM), hexane (HEX), and acetonitrile (AcN) – and (3) the relative composition of the good solvent, chloroform (CF), and poor solvents. The results are compared to those observed using rapid injection of the solvent. Miscibility gap values (Δδ) provide a reasonable justification of the assembly behavior of P3HT in the solvent mixtures in terms of the kinetics of polymer aggregation and the kinetics of solvent mixing at the interface. Atomic force microscopy (AFM) is used to analyze the morphology of films processed from dispersions with disparate characteristics, but having the same solvent composition, for example, 70:30 CF:HEX or 60:40 CF:DCM. Based on the disparity of the kinetics and miscibility gap values, the prevalence of specific structural motifs in the films, for example, spheroids (globules) and fibers, is effectively rationalized in terms of the structural attributes of the aggregates in the liquid phase rather than the evaporation rate (boiling point) differences of the solvents in the mixture. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 999–1011     

Uracil as Nucleating Agent for Bacterial Poly[(3‐Hydroxybutyrate)‐co‐(3‐hydroxyhexanoate)] Copolymers

In this study, uracil has been introduced as the nucleating agent (NA) for bacterially synthesized poly[(3‐hydroxybutyrate)‐co‐(3‐hydroxyhexanoate)] (PHBHHx) copolymers with HHx content of 5, 10, 18 mol‐%, and poly(3‐hydroxybutyrate) (PHB) homopolymer for the first time. Its effect was compared with the conventional NA of PHB, that is, boron nitride (BN), and two other naturally occurring pyrimidine derivatives, i.e., thymine and cytosine. The effects of uracil on the crystallization kinetics, melting behavior, spherulite morphology, and crystalline structure of PHBHHx and PHB were investigated by differential scanning calorimetry (DSC), polarized optical microscopy (POM), and wide‐angle X‐ray diffraction (WAXD). Uracil and BN exhibit the comparable nucleation efficiency on the crystallization of PHB, whereas uracil shows much more effective nucleation ability than BN for PHBHHx copolymers. With incorporation of 1 wt.‐% uracil, PHBHHx with 0–10 mol‐% HHx units can finish crystallization upon cooling at 10 °C · min^?1. The crystallization half‐times (t_1/2) of all the PHB and PHBHHx samples decrease significantly with presence of uracil. The crystallization rate of polymers further enhances with increase in uracil concentration. With addition of 1 wt.‐% uracil, the t_1/2 value of PHBHHx with 10 mol‐% HHx units melt‐crystallizing at 80 °C decreases to ≈4.0% of the neat polymer, and the nucleation density increases by 3–4 orders of magnitude. The incorporation of uracil has no discernable effect on the crystalline structure of PHBHHx, as evidenced by WAXD results. It was proposed that the nucleation mechanism of the uracil/PHBHHx (or PHB) system might be the epitaxial nucleation.