Abstract
We have investigated the ultrafast dynamics of aqueous polyacrylamide ([-CH2CH(CONH2)-]n, or PAAm) solutions using femtosecond optical heterodyne-detected Raman-induced Kerr effect spectroscopy (OHD-RIKES). The observed aqueous PAAm dynamics are nearly identical for both Mw = 1500 and 10 000. Aqueous propionamide (CH3CH2CONH2, or PrAm) solutions were also studied, because PrAm is an exact model for the PAAm constitutional repeat unit (CRU). The longest time scale dynamics observed for both aqueous PAAm and PrAm solutions occur in the 4-10 ps range. Over the range of concentrations from 0 to 40 wt %, the picosecond reorientation time constants for the aqueous PAAm and PrAm solutions scale linearly with the solution concentration, despite the fact that the solution shear viscosities vary exponentially from 1 to 264 cP. For a given value of solution concentration in weight percent, constant ratios of measured reorientation time constants for PAAm to PrAm are obtained. This ratio of PAAm to PrAm reorientation time constants is equal to the ratio of the volume for the PAAm constitutional repeat unit (-CH2CHCONH2-) to the molecular volume of PrAm. For these reasons, we assign the polymer reorientation dynamics to motions of the entire constitutional repeat unit, not only side group motions. Simple molecular dynamics simulations of H[-CH2CH(CONH2)-]7H in a periodic box with 180 water molecules support this assignment. Amide-amide and amide-water hydrogen-bonding interactions lead to strongly oscillatory femtosecond dynamics in the Kerr transients, peaking at 80, 410, and 750 fs.
| Original language | English |
|---|---|
| Pages (from-to) | 12877-12885 |
| Number of pages | 9 |
| Journal | Journal of the American Chemical Society |
| Volume | 123 |
| Issue number | 51 |
| DOIs | |
| Publication status | Published - Dec 26 2001 |
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ASJC Scopus subject areas
- Chemistry(all)
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Ultrafast dynamics in aqueous polyacrylamide solutions. / Shirota, H.; Castner, Ed.
In: Journal of the American Chemical Society, Vol. 123, No. 51, 26.12.2001, p. 12877-12885.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Ultrafast dynamics in aqueous polyacrylamide solutions
AU - Shirota, H.
AU - Castner, Ed
PY - 2001/12/26
Y1 - 2001/12/26
N2 - We have investigated the ultrafast dynamics of aqueous polyacrylamide ([-CH2CH(CONH2)-]n, or PAAm) solutions using femtosecond optical heterodyne-detected Raman-induced Kerr effect spectroscopy (OHD-RIKES). The observed aqueous PAAm dynamics are nearly identical for both Mw = 1500 and 10 000. Aqueous propionamide (CH3CH2CONH2, or PrAm) solutions were also studied, because PrAm is an exact model for the PAAm constitutional repeat unit (CRU). The longest time scale dynamics observed for both aqueous PAAm and PrAm solutions occur in the 4-10 ps range. Over the range of concentrations from 0 to 40 wt %, the picosecond reorientation time constants for the aqueous PAAm and PrAm solutions scale linearly with the solution concentration, despite the fact that the solution shear viscosities vary exponentially from 1 to 264 cP. For a given value of solution concentration in weight percent, constant ratios of measured reorientation time constants for PAAm to PrAm are obtained. This ratio of PAAm to PrAm reorientation time constants is equal to the ratio of the volume for the PAAm constitutional repeat unit (-CH2CHCONH2-) to the molecular volume of PrAm. For these reasons, we assign the polymer reorientation dynamics to motions of the entire constitutional repeat unit, not only side group motions. Simple molecular dynamics simulations of H[-CH2CH(CONH2)-]7H in a periodic box with 180 water molecules support this assignment. Amide-amide and amide-water hydrogen-bonding interactions lead to strongly oscillatory femtosecond dynamics in the Kerr transients, peaking at 80, 410, and 750 fs.
AB - We have investigated the ultrafast dynamics of aqueous polyacrylamide ([-CH2CH(CONH2)-]n, or PAAm) solutions using femtosecond optical heterodyne-detected Raman-induced Kerr effect spectroscopy (OHD-RIKES). The observed aqueous PAAm dynamics are nearly identical for both Mw = 1500 and 10 000. Aqueous propionamide (CH3CH2CONH2, or PrAm) solutions were also studied, because PrAm is an exact model for the PAAm constitutional repeat unit (CRU). The longest time scale dynamics observed for both aqueous PAAm and PrAm solutions occur in the 4-10 ps range. Over the range of concentrations from 0 to 40 wt %, the picosecond reorientation time constants for the aqueous PAAm and PrAm solutions scale linearly with the solution concentration, despite the fact that the solution shear viscosities vary exponentially from 1 to 264 cP. For a given value of solution concentration in weight percent, constant ratios of measured reorientation time constants for PAAm to PrAm are obtained. This ratio of PAAm to PrAm reorientation time constants is equal to the ratio of the volume for the PAAm constitutional repeat unit (-CH2CHCONH2-) to the molecular volume of PrAm. For these reasons, we assign the polymer reorientation dynamics to motions of the entire constitutional repeat unit, not only side group motions. Simple molecular dynamics simulations of H[-CH2CH(CONH2)-]7H in a periodic box with 180 water molecules support this assignment. Amide-amide and amide-water hydrogen-bonding interactions lead to strongly oscillatory femtosecond dynamics in the Kerr transients, peaking at 80, 410, and 750 fs.
UR - http://www.scopus.com/inward/record.url?scp=0035956565&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0035956565&partnerID=8YFLogxK
U2 - 10.1021/ja010290z
DO - 10.1021/ja010290z
M3 - Article
C2 - 11749546
AN - SCOPUS:0035956565
VL - 123
SP - 12877
EP - 12885
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
SN - 0002-7863
IS - 51
ER -