Picosecond acoustic measurements of longitudinal wave velocity of submicron polymer films

Lee, Yung‐Chun; Bretz, K. C.; Wise, Frank W.; Sachse, Wolfgang

doi:10.1063/1.117030

Cited by 38 publications

(31 citation statements)

References 16 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…12 Also, the propagation of acoustic waves through PMMA thin films exhibits the same velocity as in the bulk for h Ͼ 40 nm. 13 Similar observations emerge from molecular simulations of polymer nanostructures. 14,15 The overall bending modulus of the glassy nanostructures remains bulk-like until a critical dimension ͑e.g., line width͒ approaches 20 .…”

Section: Introductionsupporting

confidence: 69%

Local dynamic mechanical properties in model free-standing polymer thin films

Yoshimoto

Jain

Nealey

et al. 2005

The Journal of Chemical Physics

View full text Add to dashboard Cite

High-frequency sinusoidal oscillations of a coarse-grained polymer model are used to calculate the local dynamic mechanical properties ͑DMPs͒ of free-standing polymer thin films. The storage modulus GЈ and loss modulus GЉ are examined as a function of position normal to the free surfaces. It is found that mechanically soft layers arise near the free surfaces of glassy thin films, and that their thickness becomes comparable to the entire film thickness as the temperature approaches the glass transition T g . As a result, the overall stiffness of glassy thin films decreases with film thickness. It is also shown that two regions coexist in thin films just at the bulk T g ; a melt-like region ͑GЈ Ͻ GЉ͒ near the free surfaces and a glass-like region ͑GЈ Ͼ GЉ͒ in the middle of the film. Our findings on the existence of a heterogeneous distribution of DMPs in free-standing polymer thin films provide insights into recent experimental measurements of the mechanical properties of glassy polymer thin films.

show abstract

Section: Introductionsupporting

confidence: 69%

Local dynamic mechanical properties in model free-standing polymer thin films

Yoshimoto

Jain

Nealey

et al. 2005

The Journal of Chemical Physics

View full text Add to dashboard Cite

show abstract

“…It should also be noted here that picosecond acoustic techniques reveal an increase in the longitudinal sound velocity for thin films of poly(methyl methacrylate) and PS [40,41]. This suggests a change in the average mass density for thin films from that of bulk samples.…”

Section: B Three-layer Modelmentioning

confidence: 99%

Glass transitions and dynamics in thin polymer films: Dielectric relaxation of thin films of polystyrene

2000

View full text Add to dashboard Cite

The glass transition temperature Tg and the temperature Tα corresponding to the peak in the dielectric loss due to the α-process have been simultaneously determined as functions of film thickness d through dielectric measurements for polystyrene thin films supported on glass substrate. The dielectric loss peaks have also been investigated as functions of frequency for a given temperature. A decrease in Tg was observed with decreasing film thickness, while Tα was found to remain almost constant for d > dc and to decrease drastically with decreasing d for d < dc. Here, dc is a critical thickness dependent on molecular weight. The relaxation time τα of the α-process, which was measured as the frequency at which the dielectric loss realizes its peak value at a given temperature, was found to have a d dependence similar to that of Tα. The relaxation function for the α-process was obtained by using the observed frequency dependence of the peak profile of the dielectric loss. The exponent βKWW, which was obtained from the relaxation functions, decreases as thickness decreases. This suggests that the distribution of relaxation times for the α-process broadens with decreasing thickness. The thickness dependence of Tg is directly related to the distribution of relaxation times for the α-process, not to the relaxation time itself. The value of the thermal expansion coefficient normal to the film surface was found to increase with decreasing film thickness below Tg, but to decrease with decreasing film thickness above Tg. These experimental results are discussed in the context of a three-layer model in which within thin films there are three layers with different mobilities and glass transition temperatures.

show abstract

“…The dimension dependence of the glass transition temperature ͑T g ͒ of free standing and supported ultra thin polymer films have been described extensively in the literature, [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] and there are some reports of dimension dependent transport 16 -20 and mechanical properties [21][22][23][24] in nanoscale polymeric systems as well. In most commercial applications of films and coatings, the thickness of the polymer does not approach the sub-100 nm scale and the phenomena referred to above do not affect the properties, processing, and usefulness of the materials.…”

Section: Introductionmentioning

confidence: 99%

Extraordinary elevation of the glass transition temperature of thin polymer films grafted to silicon oxide substrates

Tate¹,

Fryer

Pasqualini

et al. 2001

The Journal of Chemical Physics

141

127

View full text Add to dashboard Cite

We used local thermal analysis and ellipsometry to measure the glass transition temperatures (T g ) of supported thin films of poly͑4-hydroxystyrene͒ ͑PHS͒ and hydroxy terminated polystyrene ͑PS-OH͒. The films were spuncast from solution onto silicon oxide substrates and annealed under vacuum at elevated temperatures to graft the polymer to the substrate. Grafting was verified and characterized in terms of the thickness of and the advancing contact angle of water on the residual layer after solvent extraction. For PHS, each segment of the polymer chain was capable of grafting to the substrate. The thickness of the residual layer increased with increasing annealing temperature. For this polymer the critical thickness below which the T g of the film deviated from the bulk value was nearly 200 nm after annealing at the highest temperature ͑190°C͒; the T g of films 100 nm thick or less were elevated by more than 50°C above the bulk value. For PS-OH films the polymer was only capable of grafting at one chain end, forming a brush layer at the substrate interface. The critical thicknesses for PS-OH films and the T g elevations were substantially higher than for ungrafted PS films, but were not as large as for PHS. The film thickness dependence of T g for PHS and PS-OH were well described as piecewise linear, consistent with a ''dual-mechanism'' model.

show abstract

Picosecond acoustic measurements of longitudinal wave velocity of submicron polymer films

Abstract: Elastic wave contributions in highresolution acoustic images of fluidfilled, finite cylindrical shells in water

Cited by 38 publications

References 16 publications

Local dynamic mechanical properties in model free-standing polymer thin films

Local dynamic mechanical properties in model free-standing polymer thin films

Glass transitions and dynamics in thin polymer films: Dielectric relaxation of thin films of polystyrene

Extraordinary elevation of the glass transition temperature of thin polymer films grafted to silicon oxide substrates

Contact Info

Product

Resources

About