Glassy Dynamics in Thin Polymer Layers Having a Free Upper Interface

Serghei, Anatoli; Huth, Heiko; Schick, Christoph; Kremer, Friedrich

doi:10.1021/ma702381t

Cited by 141 publications

(124 citation statements)

References 30 publications

(59 reference statements)

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“…These features are consistent with the results of dielectric spectroscopy, in which a clear frequency dependence of the glass transition is presented. 21,26 Figure 4 shows the temperature dependence of thickness when the samples were heated at a rate of 0. Figure 7 shows the logarithm of w plotted as a function of reciprocal thickness 1/h.…”

Section: Resultsmentioning

confidence: 99%

“…20 However, such variation of the width of the glass transition was not observed in another dielectric loss study conducted at lower frequencies (0.12 and 0.01 Hz). 21 Ellipsometric measurements taken at various cooling rates for supported PS thin films have revealed that the width of the glass transition is almost independent of film thickness at a fast cooling rate (130 1C min À1 ), whereas measurements taken at slower cooling rates (1 and 3 1C min À1 ) show the width of the glass transition broadening with decreasing thickness. 22 Study of faster dynamics using a calorimeter, with ultrafast heating rates ranging from 1.8Â10 6 to 2.4Â10 6 1C min À1 , has revealed that the width of the transition at this rate becomes broader as the thickness decreases.…”

Section: Introductionmentioning

confidence: 99%

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Broadening, no broadening and narrowing of glass transition of supported polystyrene ultrathin films emerging under ultraslow temperature variations

Yang

Takahashi

2011

Polym J

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We report X-ray reflectivity measurements of polystyrene thin films supported on Si substrates at various heating and cooling rates. At a heating rate of 0.05 1C min À1 , the width of the glass transition w does not show any noticeable thickness dependence. However, at faster (0.5 1C min À1 ) and slower (0.01 1C min À1 ) heating rates, w shows remarkable thickness dependence: it broadens at a faster rate and narrows at a slower rate with decreasing film thickness. Our results suggest that the heterogeneous character of the dynamics can be transformed into a homogeneous one in a glassy film with thickness comparable to a critical thickness that depends on the rate of temperature variation. Polymer Journal (2011) 43, 390-397; doi:10.1038/pj.2010.145; published online 19 January 2011Keywords: confinement effects; glass transition; polymer thin films; transition breadth; transition broadening; X-ray reflection INTRODUCTIONThe molecular dynamics in liquid, especially close to and below the glass transition temperature T g , are very heterogeneous. 1 From a theoretical viewpoint in which the mean structural relaxation in glassy systems occurs through rearrangements of correlated particles, the spatial particle region surrounded by other subsystems composed of particles with differing mobilities is called a cooperatively rearranging region. 2,3 Because of the dynamic heterogeneity, temporal relaxations depend on the subsystems, and the glass transition generally occurs within a certain temperature range called the width of glass transition w. Polymers confined in a particular size of cooperatively rearranging region can be good candidates for investigating the spatial size of dynamic heterogeneities. A striking result in confined systems is that T g of thin films often exhibits a remarkable thickness dependence. 4,5 This result strongly suggests that interfaces in a confined system have an important role. Many studies have revealed the properties of interfacial regions and have provided extensive evidence that the molecular mobility is much higher in the free surface region than in the bulk region at the same temperature; 6-9 dynamics near the free surface are very fast. On the other hand, the interaction between a polymer and a solid substrate can suppress molecular relaxation in an interfacial region, leading to peculiar slower dynamics in this region. [9][10][11][12][13] Measurements of the relaxation rate using a 20-nm-thick fluorescently labeled layer that has been incorporated into polymer films have revealed that the rate of dynamics depends on the distance from both the free surface and the interface. These dynamics vary continuously, exhibiting bulk-like characteristics toward the interior layer sandwiched between the surface and the interfacial layers. 9

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Broadening, no broadening and narrowing of glass transition of supported polystyrene ultrathin films emerging under ultraslow temperature variations

Yang

Takahashi

2011

Polym J

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“…For example, recent experiments focusing on molecular dynamics in thin polymer layers with a free upper interface revealed no shifts in the average relaxation time and no broadening of the dynamic glass-transition for PS down to film thicknesses of ∼10 nm. 62 Therefore, the decoupling of confinement effects 63 from the change in the solvent content per the area of the polymer film might be necessary. For applications, it is comforting that the total remaining solvent in the polymers remains unchanged over long amounts of time (up to years) if no postproduction treatment is applied.…”

Section: Solvent Enrichment At Polymer/substrate Interfacementioning

confidence: 99%

Solvent Content in Thin Spin-Coated Polystyrene Homopolymer Films

et al. 2008

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The solvent content of thin polystyrene (PS) films, spin-coated from protonated and deuterated toluene onto silicon substrates, is investigated. Neutron reflectometry (NR) is used to probe the total remaining solvent inside the PS films in a nondestructive and noninvasive way. In freshly prepared films, the investigated parameters are the molecular weight of PS and the total film thickness. Moreover, the effect of postproduction treatment by annealing at temperatures below and above the glass transition of PS as well as long-term storage over 2 years are examined to deduce the reduction of the remaining solvent. The remaining solvent content increases with increasing molecular weight and with increasing film thickness. An enrichment of toluene at the Si/polymer interface is found. Under the different annealing and storage conditions tested, the remaining solvent is not totally removed. The observed behavior is discussed in the framework of polymer thin films and compared with results obtained by alternative experimental approaches.

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“…In fact, this is in agreement with what is known in the literature about reorganization and rearrangements of functional groups on polymer surfaces, i.e., it occurs by the exchange and movement of chemical groups between the top surface layers over a distance of only a few nm. [ 30,31 ] Note also that, if the segregation at the particle interface is less than predicted, the minimum thickness of polymer for selfreplenishing may be even smaller.…”

Section: Multiple Self-replenishing: Depth Of Damage and Minimum Polymentioning

confidence: 96%

Simulation‐Experimental Approach to Investigate the Role of Interfaces in Self‐Replenishing Composite Coatings

Lyakhova

Esteves

Put

et al. 2014

Adv Materials Inter

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which changes their surface characteristics and compromises their performance.One way to increase the durability of functional coatings is to create a system which is able to relocate the low surface energy groups at the damaged surfaces and recover the low surface energy properties, i.e., to introduce a self-healing function. In the case of surface-structured coatings, the repair of the surface roughness is an additional challenge. [ 5,6 ] One of the possible solutions reported by Li et al., [ 7 ] is the creation of a porous polymer coating with micro-and nano-scale structures, for which the 'healing agent' consists of a low surface energy component previously impregnated in the porous layer. After damage, this component migrates to the new porous coating surface restoring its (super)hydrophobicity when exposed to a humid environment. Another possibility is to encapsulate a surface-active material in nano-containers [ 8 ] which will be released at the surface upon damage. The self-organization of colloidal particles at interfaces has also been used to design materials with surface-healing properties by embedding colloidal silica particles in a perfl uorinated wax. [ 9,10 ] Upon damage and an annealing step (at 60 °C), the wax melts and the particles migrate to the surface, recreating a new topography covered by the waxy layer. [ 9 ] Recently, a surface-healing approach was reported by our group [ 11 ] which uses a polymer network that is able to replenish damaged surfaces with low surface energy components, autonomously and at room temperature. Perfl uoro-alkyl-terminated dangling chains connected to a poly(ester urethane) crosslinked network are able to spontaneously re-orient to new air interfaces created by damage. A polymeric spacer was included in the dangling chains in order to control their mobility and ensure surface reorientation, but also to provide the proper miscibility with the bulk network and avoid complete surface segregation. [ 11 ] This self-replenishing principle can be applied to recover surface properties such as hydrophobicity. However, for structured surfaces topography needs to be equally repaired or recreated. Hence we applied the self-replenishing principle on polymer layers with dual-scale roughness, [ 12 ] created by introducing inorganic nanoparticles with two different sizes (≈70/700 nm). For this system a multi-scale surface roughness is re-created by the damage, while the polymer layer between the particles serves as the source of low surface energy To investigate self-replenishing on surface-structured composite coatings a dual simulation-experimental approach is employed to study the decisive role of polymer-air and polymer-particle interfaces. Experimentally, the composite system consists of a cross-linked polymer network with fl uorinated-dangling chains, embedding colloidal SiO 2 nanoparticles which are incorporated in the network via covalent bonding. These particles provide the desired surface structure at the air-interface before and after damage. Any damage replicates the...

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Glassy Dynamics in Thin Polymer Layers Having a Free Upper Interface

Cited by 141 publications

References 30 publications

Broadening, no broadening and narrowing of glass transition of supported polystyrene ultrathin films emerging under ultraslow temperature variations

Broadening, no broadening and narrowing of glass transition of supported polystyrene ultrathin films emerging under ultraslow temperature variations

Solvent Content in Thin Spin-Coated Polystyrene Homopolymer Films

Simulation‐Experimental Approach to Investigate the Role of Interfaces in Self‐Replenishing Composite Coatings

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