Showing papers by "Olli Ikkala published in 1997"
TL;DR: In this paper, a three dimensional continuous space Monte Carlo computer simulation study is presented to discuss the extension of flexible, linear polymer chains due to the presence of equally flexible side chains.
Abstract: A three dimensional continuous space Monte Carlo computer simulation study is presented to discuss the extension of flexible, linear polymer chains due to the presence of equally flexible side chains. We consider the enhancement of the persistence length of bottle-brush structures in an athermal solution due to steric interactions between the side chains, The largest structure studied consists of a backbone of 100 beads with 50 side chains of 20 beads each, The persistence length lambda is evaluated in two different ways using the radius of gyration of the backbone and the bond angle correlation function, respectively. A correct description of the backbone conformations is shown to require at least two characteristic lengths. At a small length scale the backbone behaves flexible; the extension occurs at a larger length scale. There is a strong indication that the ratio between the persistence length and the diameter, which is the determining factor for lyotropic behavior of conventional semiflexible chains, levels off as a function of the side chain length. The value of this ratio is, moreover, too small to induce lyotropic behavior along this line. Recent experimental observations of lyotropic behavior of polymacromonomers are discussed in terms of these findings. (C) 1997 American Institute of Physics.
120 citations
TL;DR: In this paper, the authors used dynamic mechanical spectroscopy (DMS) to further investigate the recently observed order-disorder transition (ODT) in comblike block copolymers obtained by hydrogen bonding between poly(4-vinylpyridine) and pentadecylphenol (P4VP-PDPx).
Abstract: Dynamic mechanical spectroscopy (DMS) is used to further investigate the recently observed order-disorder transition (ODT) in comblike block copolymers obtained by hydrogen bonding between poly(4-vinylpyridine) and pentadecylphenol (P4VP-PDPx). For stoichiometric amounts of pyridine and phenol, i.e., z = 1.0, the ODT to a lamellar structure occurs at T similar or equal to 65 degrees C. The dynamic moduli G' and G '' simultaneously show a crossover from a liquidlike behavior (G' similar to omega(1.5) and G '' similar to omega) to a response intermediate between a Newtonian fluid and a solid (G' approximate to G'' similar to omega(1/2)). The behavior above T-ODT differs slightly from a homopolymer melt (G' similar to omega(2.0)) due to composition fluctuations, whereas the behavior below T-ODT is characteristic for quenched block copolymer lamellar phases with local uniaxial order and global isotropy. Near room temperature, a transition to solid behavior (G similar to omega(0)) takes place due to crystallization of the alkyl side chains. Larger amounts of PDP lower the T-ODT temperature, and for x = 2.0 the transition to solid response occurs directly from the disordered state. Small and wide angle X-ray scattering (SAXS and WAXS) experiments and differential scanning calorimetry (DSC) corroborate these findings. Furthermore, SAXS and WAXS demonstrate that the low-temperature state of P4VP-PDP2.0 is not stable and indicate that ultimately macrophase separation into a pure crystalline PDP phase and a microphase separated P4VP-PDP phase occurs.
101 citations
TL;DR: In this paper, it was shown that PANI doped by methanesulphonic acid, toluenesulpnonic acid and camphorsulphonics acid can be plasticized by dihydroxybenzenes and bisphenols to obtain fusible particle-free films at the resolution of optical microscope.
71 citations
TL;DR: In this article, the authors demonstrate thermoreversible gelation of a conductive polymer, i.e., rubber-like melt processible electrically conducting compounds, using a combination of viscoelastic and electrical conductivity.
Abstract: We demonstrate thermoreversible gelation of a conductive polymer, i.e., rubber-like melt processible electrically conducting compounds. Combination of viscoelastic and electrical conductivity measu...
62 citations
TL;DR: In this article, the concentration fluctuations in comblike copolymer systems obtained by hydrogen bonding between polymers and end-functionalized oligomers were investigated, and it was shown that the dominant fluctuations vary experimentally between conventional long wavelength fluctuations (for weak hydrogen bonding) and finite wavelength fluctuation (strong hydrogen bonding).
Abstract: This paper addresses concentration fluctuations in comblike copolymer systems obtained by hydrogen bonding between polymers and end-functionalized oligomers. Monodisperse block copolymer systems in the homogeneous melt exhibit small-angle X-ray scattering peaks at finite nonzero angle due to characteristic correlation hole concentration fluctuations. In comblike copolymer systems obtained by hydrogen bonding, the dominant fluctuations have been found by us to vary experimentally between conventional long wavelength fluctuations (for weak hydrogen bonding) and finite wavelength fluctuations (strong hydrogen bonding). Monte Carlo computer simulations show that both regimes occur in one and the same system depending on the temperature. The transition between both regimes is directly related to the fraction of free oligomers, which depends on the temperature and the interactions. The structure factors are analyzed in terms of the random phase approximation applied to a mixture of free oligomers and comb copolymers, using a uniform distribution of teeth along the polymer chains and a binomial distribution in the number of polymers with a given number of teeth, confirmed numerically, as input. The agreement is excellent at both high and low temperatures.
39 citations
TL;DR: In this article, a surface active comb-shaped macrosalt is rendered, whose phase continuity in blends of nonpolar polymers can be tailored by their viscosity ratio, as in conventional polymer blends.
9 citations
TL;DR: In this article, conditions to obtain micro-phase separated morphologies in polymer-surfactant systems involving hydrogen bonds have been investigated using poly(4-vinyl pyridine) (P4VP) and surfactants capable of forming hydrogen bonds of different strength with the basic nitrogen of P4VP.
Abstract: Conditions to obtain micro-phase separated morphologies in polymer-surfactant systems involving hydrogen bonds have been investigated using poly(4-vinyl pyridine) (P4VP) and surfactants capable of forming hydrogen bonds of different strength with the basic nitrogen of P4VP. Depending on the tail length, the hydrogen bonding strength, the amount of surfactant and the temperature, four different regimes have been identified: I. Micro-phase separated state, II. Homogeneous state exhibiting a distinct Small Angle X-ray Scattering (SAXS) peak, III. Homogeneous state without a SAXS peak and, IV. Macro-phase separated state. Time-resolved SAXS / W(ide) A(angle) X(ray) S(cattering)/ D(ifferential) S(canning) C(alorimetry) as well as rheological measurements are used to identify the different regimes. A simplified model description together with preliminary computer simulation results are presented.
8 citations
TL;DR: In this paper, it was shown that less acidic solvents and plasticizers can be found based on phenylphenyl-phenyl interactions in combination with hydrogen bonding, where the requirement is that the interactions are strong enough and, importantly, sterically match the complementary moieties of the sulphonic acid doped PANI.
Abstract: Polyaniline (PANI) is known to dissolve in strong acids, such as sulphonic acids PANI, in its electrically conductive form, is generally regarded to be poorly soluble in low-acidic solvents and to be infusible, closely resembling fully aromatic rigid rod polymers We show that “less” acidic solvents and plasticizers can be found based on phenyl-phenyl interactions in combination with hydrogen bonding The requirement is that the interactions are strong enough and, importantly, sterically match the complementary moieties of the sulphonic acid doped PANI Dihydroxybenzenes and bisphenols are examples of such low-acidic compounds This type of molecular recognition allows solution and melt processibility of PANI doped by generic sulphonic acid, such as methanesulphonic acid or alkylbenzenesulphonic acid Molecular recognition is also offered as an explanation for the previously observed high solubility of camphorsulphonic acid (CSA) doped PANI in phenols
5 citations
TL;DR: In this article, the authors demonstrate that polyaniline (PANI) dissolved in dodecyl benzene sulphonic acid (DBSA) shows thermoreversible gelation, which suggests reversible, i.e. fusible, network formation.
Abstract: We demonstrate that polyaniline (PANI) dissolved in dodecyl benzene sulphonic acid (DBSA) shows thermoreversible gelation. The dissolution has been performed in formic acid which allows particle-free complexes according to optical microscopy. Below the gelation temperature the materials are rubber-elastic in compression experiments, the storage modulus Gs' does not essentially depend on frequency, and the samples are electronically conductive. Above the gelation temperature, G' indicates flow-like behavior and drastically lower ionic conductivity is observed. These results suggest reversible, i.e. fusible, network formation. The properties are compared with gels consisting of camphor sulphonic acid (CSA) doped PANI dissolved in m-cresol which are poorly thermoreversible.
3 citations
Journal Article•
TL;DR: In this article, a review of molecular bottlebrushes obtained by hydrogen bonding between homopolymers and end-functionalized oligomers is presented, focusing on the possibility of lyotropic behavior and the role of reversibility of noncovalent bonding.
Abstract: In this review 'molecular bottlebrushes' are flexible polymers densely loaded with equally flexible side chains Interest in these structures arises from the possibility of lyotropic behaviour in dilute solution in a good solvent, as well as the possibility of highly ordered microphase-separated states in the melt In addition, supramolecular chemistry has led to alternative and often much simpler ways of synthesizing complex polymer architectures Here we will concentrate on molecular bottlebrushes obtained by hydrogen bonding between homopolymers and end-functionalized oligomers, and address their complex phase behaviour Particular attention will be given to the possibility of lyotropic behaviour and to the role of the reversibility of the noncovalent bonding The coupling between micro- and macrophase separation and the possibility of various Lifshitz points will also be discussed
3 citations