title: The effects of moisture on the dielectric relaxation of urethane dimethacrylate polymer and composites.
abstract: Dielectric characterization evaluated the influence of sorbed moisture on urethane dimethacrylate (UDMA) polymer matrix and unsilanated and silanated zirconia-silica (ZS)-filled UDMA composites. The moisture content (MC) of samples tested ranged from 0 to 7.32% with maximum values for UDMA, silanated and unsilanated ZS-filled UDMA were 3.72, 6.0 and 7.32%, respectively. Dielectric spectra were measured from 0.053 to 100 kHz and from -180 to 180;C. Small MC stiffened the polymers, which was shown by a shift of beta-peaks to higher temperatures, a decrease in the half width of bands and an increase in the change of activation energies. Higher MC resulted in water plasticizing the polymer by shifting the beta-peaks to lower temperatures. Maximum water sorption restricted the motion of the polymer chains and the b-peaks shifted to higher temperatures. Further, increasing MC shifted the a-relaxation to lower temperatures in both UDMA and composites. However, in composites with unsilanated ZS, a new relaxation occurred at high temperatures and low frequencies which was attributed to Maxwell-Wagner-Sillars (MWS) polarization. Thus, in UDMA, water occurs as fragments that form non-freezing clusters. However, in unsilanated ZS-UDMA composites, bulk water can exist at the polymer-filler interface and form disordered structures of ice at low temperatures which can evaporate at high temperatures. Silanated ZS-UDMA composites function similarly to UDMA at low MC but are more plasticized at high temperatures.
authors.affiliation: Sheffield Pharmaceuticals Inc., Ann Arbor, U.S.A; School of Dentistry, University of Michigan, Ann Arbor, USA.
authors.forename: N M
authors.initials: NM
authors.lastname: Mohsen
authors.forename: R G
authors.initials: RG
authors.lastname: Craig
authors.forename: F E
authors.initials: FE
authors.lastname: Filisko
mesh_terms: D000042:Absorption; D003188:Composite Resins / Q000737:chemistry*; D004553:Electric Conductivity; D006860:Hydrogen Bonding; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry*; D011140:Polyurethanes / Q000737:chemistry*; D012821:Silanes / Q000737:chemistry; D012822:Silicon Dioxide / Q000737:chemistry; D014867:Water / Q000737:chemistry; D015040:Zirconium / Q000737:chemistry
chemical_list: D003188:Composite Resins; D008689:Methacrylates; D011140:Polyurethanes; D012821:Silanes; D014867:Water; C029824:urethane dimethacrylate luting resin; D012822:Silicon Dioxide; D015040:Zirconium; C028541:zirconium oxide