Solid state 1H NMR study, humidity sensitivity and protonic conduction of gel derived phosphosilicate glasses

Abstract

H Magic Angle Spinning (MAS) NMR and 1 H T 1 and T 1r relaxation times measurements were used to investigate structural aspects of gel derived glasses of composition 10P 2 O 5 ?90SiO 2 (10P) and 30P 2 O 5 ?70SiO 2 (30P), with the aim of understanding the different humidity sensitive behaviour observed for films of the same composition. The experimental evidence suggests that 10P and 30P gel samples heat treated at 100 uC have a similar POH environment while further heating causes a different structural evolution of POH units. In particular, the 30P sample heat treated at 400 uC shows a single 1 H resonance while a number of resonances are seen in the 1 H spectrum of the 10P sample heat treated at 400 uC. Further evidence of the different structure of 10P and 30P samples was given by the NMR relaxation times measurements, the gels were found to be heterogeneous on a nanometric scale. Domains, about 60 nm in size, related to 1 H resonance in POH were evenly distributed in the matrix of both gels, only in the 10P gel also larger domains (about 700 nm) were found that can be related to 1 H resonance in SiOH groups. Finally, MAS in combination with variable temperature static NMR spectra provided detailed information on the network structural features present in the 30P sample heat treated at 300 uC as well as in the 10P sample heat treated at 400 uC and allowed investigation of the dynamic processes taking place in these samples.

Solid state NMR study of phosphosilicate gels

“…3 observed values imply a stronger interaction between the Q 0 0 and Q 0 1 units in the 30P-100 siloxane network than in the 10P-100 sample [7]. These results together with the above 29 Si-31 P MAS NMR data that exclude the formation of P-O-Si bonds at this stage of the heat treatment, confirm a picture of the dried gels as a siloxane framework with trapped un-reacted molecules of phosphoric and pyrophosphoric acid.…”

“…The probe is of a double bearing design using 4 mm zirconia rotors [6]. All spectra were acquired with fully loaded rotors using single pulse excitation [7].…”

Multinuclear NMR study of phosphosilicate gels derived from POCl3 and Si(OC2H5)4

“…Of particular interest all the samples show similar 1 H MAS NMR spectra regardless of the phosphorus content, unlike the earlier set of phosphosilicate gels [16]. Moreover, the nature of the 1 H NMR spectrum, a single narrow resonance, with a linewidth of less than 100 Hz, shows that a fast dynamic process must be present to average the large 1 H-1 H dipolar couplings associated with the water present.…”

“…Moreover, this sensitivity to humidity was influenced by the phosphorus content, with the higher phosphorus content films having a lower electrical resistance [16]. The differing behavior of the above gels was also evident in the 1 H MAS NMR spectra where the higher phosphorus content sample gave a single 1 H NMR resonance indicative of fast 1 H exchange while the lower phosphorus content sample showed a number of discrete resonances [16]. Further differences in the structure of the gels were revealed by solid state 29 Si and 31 P MAS NMR spectra [8].…”

Formation of six-coordinated silicon in calcium phosphosilicate xerogels assisted by polyols at low temperature and pressure

“…Phosphosilicates exhibit interesting technological and structural properties, which can find applications in fast proton conductors and biomedical materials, such as vehicles for antimicrobial agents, filler and fibers suitable for tissue engineering applications [1][2][3][4]. A special feature of phosphosilicates is the occurrence of hyper-coordinated silicon centers, such as five-or six-coordinated, which is normally dependent on their chemical compositions [5][6][7].…”